Power down the PC and all attached devices. Disconnect all external cables other than the power cord, noting which cable connects to which port. Then move the PC to your work area and remove the cover from the case. We can attest that one wayward case screw can destroy a vacuum cleaner, so put the screws safely aside. An old egg carton or ice cube tray makes a good parts organizer.

If the PC power cord is connected to an outlet strip, surge suppressor, or UPS, turn off the main power switch on that device, and turn off the main PC power switch as well. This removes power from the PC, but leaves the PC grounded.

With nearly all AT form factor power supplies and motherboards, turning off the PC power switch actually removes all power from the motherboard. With newer ATX (and variants) power supplies and motherboards, turning off the main PC power switch leaves some power flowing to the motherboard, which supports such features as Wake-on-Ring (WOR), Wake-on-LAN (WOL), and Suspend to RAM (STR). Although the voltage present is much too small to cause personal injury, working on a powered ATX motherboard may damage the motherboard, CPU, memory, or other components. Best practice when working on ATX motherboards is to use an outlet strip or other device to remove power from the PC entirely. If you must work on an ATX motherboard and have no such device, disconnect the power cord from the wall receptacle before beginning work. To avoid damaging components, touch the power supply to ground yourself before handling the motherboard, CPU, memory, or other static-sensitive components.

Note the position and orientation of each internal cable connected to an expansion card. If necessary, sketch or photograph the connections to make sure you can reconnect the cables as they were, and then remove those cables on the expansion card. Remove the expansion cards and set them aside, preferably on an anti-static surface, although a plain table top works fine. Alternatively, you may be able to leave the cables connected to the expansion cards and simply place the cards out of the way, perhaps balanced on top of the power supply.

Label and disconnect each cable that connects to the system board, including those to the power supply, to the front-panel switches and LEDs, to back-panel I/O ports, and to fans. When you complete this step, the motherboard should not have any obvious connections other than the mounting screws.

In most cases, the motherboard mounts directly to a fixed part of the chassis. In some cases, the motherboard mounts to a removable tray. If your motherboard uses a tray, remove the screws that secure the tray to the chassis and then lift the tray out carefully, watching for overlooked cable connections. Depending on the motherboard form factor, there may be from three to eight screws securing the motherboard to the chassis or tray. One or more screw holes may be occupied by nylon spacers that snap in from the bottom of the motherboard and slide into slots in the chassis. If the motherboard is secured only by screws, remove all of them and then attempt to remove the motherboard by lifting gently straight up. If one or more nylon spacers are present (visible as small white nubs sticking up through screw holes), rather than lifting the motherboard straight up, slide it gently a fraction of an inch toward the left side of the chassis and then lift straight up.

Place the old motherboard flat on a anti-static surface. Lacking that, put it on the table top. If you are salvaging the CPU or memory, ground yourself and remove those components. In any case, store the old motherboard in the anti-static bag that the new motherboard arrived in, once that bag is available.

Touch the PC power supply to ground yourself, and then open the anti-static bag that contains the new motherboard. Remove the new motherboard from its anti-static bag, place the bag on a flat surface, and place the motherboard on top of the anti-static bag.

If you haven't done so already, read the motherboard manual to determine how to configure it. Verify each diagram in the manual against the actual motherboard to ensure that you can identify the important switches, jumpers, and connectors.

Configure the motherboard according to the instructions in the manual. Recent motherboards may use only one or a few configuration jumpers. Older technology motherboards, especially Socket 7 motherboards, may use many jumpers to set numerous options, including CPU speed, host-bus speed, CPU voltage, etc. Make sure to set all of these jumpers correctly, especially those that control voltage, before you apply power to the board.

After you have set all configuration jumpers properly, install the CPU and memory according to the instructions supplied with the motherboard and/or the components.

Determine how the motherboard mounts to the chassis. Old motherboards often used several snap-in nylon standoff spacers and only a few screws to secure the motherboard. Modern motherboards use all or mostly screws, which secure to brass standoff spacers. The important issue is whether a given hole location in the motherboard is designed to be grounded or not. If so, it will mount with a screw to a conductive brass standoff spacer. If not, it will mount using a nonconductive nylon standoff spacer. Using a conductive brass connector where an insulating nylon connector was intended can short out and destroy the motherboard. Using a nylon connector where a brass connector was intended can cause the motherboard to operate improperly or not at all, or to radiate excessive RFI. New motherboards come with a plastic bag that contains screws and standoff spacers of the proper type. If yours does not and you are not sure which type is required, refer to the motherboard documentation or contact technical support.

Hold the motherboard over the chassis in the position that you will mount it. Typically all or all but one of the holes in the motherboard align with a standoff spacer installed in the chassis. The motherboard is secured to the chassis by passing a screw through each of the motherboard screw holes and into the matching standoff spacer. The final hole, usually the one nearest the back left corner of the motherboard, may use a slide-in spacer rather than a screw, which makes it easier to line up the motherboard with the other standoff spacers. Most cases have many more mounting holes than are needed to secure any particular motherboard. Visually align the holes actually present in the motherboard with the chassis to determine which subset of the chassis mounting holes will actually be used. If you are building a new system, thread brass standoff spacers into the appropriate chassis mounting holes. If you are replacing a motherboard, spacers may already be mounted in most or all of the necessary locations. Add or relocate spacers as necessary to ensure that each hole in the motherboard has a matching spacer. Don't leave any motherboard mounting holes unused. It's not that the motherboard is likely to go anywhere if you don't use all the screws, but each of those mounting holes provides support for the motherboard at a key location. If you leave one or more of the mounting holes unsupported, the motherboard may crack later when you are pressing hard to seat an expansion card, CPU, or memory module.

When installing a Slot 1 motherboard that uses an old-style retention mechanism that must be installed before the motherboard is mounted in the case, now is the time to install it. Most new-style retention mechanisms can be installed either before or after the motherboard is mounted, and many Slot 1 motherboards come with a folding retention mechanism already installed, which requires only raising the arms to vertical and locking them in place.

After you've installed all necessary standoff spacers, slide the motherboard into position, aligning all holes with their matching spacers. Secure the motherboard using the screws provided with it, or the screws that secured the original motherboard.

Reconnect the cables, including power supply cable(s), ATA cable(s), floppy drive cable, the cables that link the motherboard to front-panel switches and LEDs, and the cables that link the motherboard I/O ports to the back-panel connectors.

Reinstall only the expansion cards needed to test the system (usually just the video card), reconnect any cables that connect to them, and then reconnect the external cables that link the system unit to the monitor, keyboard, mouse, and so on.

Verify that everything that needs to be connected is connected, that everything is connected to the right thing, and that you haven't left any tools where they might short something out.

Time for the smoke test. Turn on the monitor and then turn on power to the system unit. The BIOS boot screen should appear on your monitor. If no video appears, or if you hear a beep sequence other than the normal single startup beep, you have something misconfigured. Turn off the power immediately (or just pull the power cord) and recheck all connections and settings you've made.

Once you're satisfied that the system is working properly, shut it down, remove power from it, reinstall any additional expansion cards, and restart the system.

When the system begins a normal boot sequence, press whatever key the BIOS boot screen prompts you to press to enter CMOS Setup. If you have jumpered the motherboard in configuration mode, special CMOS Setup options (e.g., setting CPU speed or voltages) may be available now that will no longer be available once you rejumper the motherboard for normal operation. Configure and save the CMOS Setup options, and then turn off power to the system.

If necessary, rejumper the motherboard for normal operation and then restart the system. Verify proper system operation, particularly that the system recognizes the hard drive(s) you have installed. Once you are sure that the system is working as expected, shut it down, reinstall the case cover, restart the system, and begin installing your operating system and applications.