15.6 Troubleshooting Video Adapter Problems

If you experience video problems, first check the obvious things—that the monitor has power and is connected properly to the adapter, that no one has changed settings on the monitor, and so on. If you have another monitor handy, try connecting it to the problem system to eliminate the monitor as a possible cause.

Once you eliminate those possible causes, the next consideration is whether you've made any recent changes to your video hardware, software, or configuration. If so, that is a likely cause. Sometimes, problems caused by such a change doesn't manifest immediately. We have, for example, seen an updated driver function perfectly until one particular program was loaded or another piece of hardware was installed, which caused the system to crash and burn horribly.

That means the next step is to change video drivers. If a later driver is available, download and install it. If no later driver is available, try reinstalling the current driver. If problems manifest soon after installing an updated driver, try re-installing the older driver.

Once they are installed and running properly, video adapters seldom fail, short of something like a lightning strike or abusing the adapter by overclocking it. Over twenty years' experience with hundreds of systems, we remember only a few instances when a functioning video adapter just died. Hardware failures are more likely today, not because newer video adapters are inferior to their parents, but because they're now pushed harder. High-end video adapters nowadays come with at least a heatsink for the graphics processor, and it's not unusual to see a video adapter on a gamer's system with a fan or even a Peltier cooler installed. If you install a high-performance adapter, make absolutely certain that the fan, if any, has power, and that there is free air flow to the heatsink. Many video problems on systems so equipped are due to simple overheating.

Here are some specific problems you may encounter and how to remedy them:

Windows 9X displays only 640 x 480 with 16 colors, with no higher options available

Windows is using the standard VGA driver. If Windows 9X cannot detect the display adapter type when it is installed, it installs the vanilla VGA driver. Windows may have been installed or reinstalled improperly, or the display adapter may have been deleted in Device Manager, and Windows did not successfully detect the video adapter the last time it was restarted. If the color palette has options above 16, but the desktop area is fixed at 640 x 480, the monitor type may be incorrect or missing. To solve this problem, install the correct drivers for the video adapter and/or monitor.

The Windows 9X startup splash screen displays properly, but the desktop does not

This problem is also caused by incorrect video drivers or configuration errors. The startup screen is a low-resolution image that is displayed at standard VGA settings. To solve the problem, restart the system in Safe Mode, and reinstall or reconfigure the drivers for the video adapter and/or monitor.

Icons display incorrectly or as black squares

One likely cause is a corrupted ShellIconCache file, a problem that occurs frequently on systems running IE4 and TweakUI, but is by no means limited to that environment. To solve this problem under Windows 9X or NT, uninstall TweakUI (if it is installed), then delete or rename ShellIconCache (in the Windows directory) and restart the system, which automatically rebuilds the ShellIconCache file. Alternatively, view Display Properties Appearance. In the Item drop-down list, select Icon. Use the Size spinner to change the icon size one step up or down and click Apply to save the change. Change the icon size back to its original value and click OK to save the change and exit the dialog. This process forces Windows to rebuild ShellIconCache. Icon display problems sometimes also occur on Windows NT 4 systems running early builds, a situation that is easily solved by installing the latest service pack. Finally, we have seen this behavior caused on one system by overheating. In that case, the icons displayed normally for some time after the system was started, but turned into black boxes after the system had been running for some time. Cleaning the dust out of the system and installing a supplemental cooling fan made the problem go away, and it has never returned.

The monitor displays random black or parti-colored blocks

These screen artifacts may appear only when using certain combinations of resolution and color depth, and are not affected by mouse movement or by running a different application. They may be persistent or may appear and disappear seemingly at random. This problem is a result of malfunctioning video memory. Possible causes include: upgrading an adapter with slow or mismatched memory; overclocking an adapter; improperly seated memory modules or corroded connectors; and the video adapter not being fully seated. If you are overclocking the adapter, stop doing so and see if the problem goes away. If the adapter is out of warranty and at least a year or two old, consider replacing it. Even inexpensive current adapters greatly outperform anything of that vintage. If you decide to troubleshoot the problem, observe anti-static precautions. Remove and reseat the adapter in its original slot. If it is a PCI adapter, try moving it to another slot. Use your thumb to press gently on each chip or memory module to ensure it is fully seated. If the adapter uses memory modules, remove and reseat each of them, although this may be impractical if the modules require special tools. Use rubbing alcohol or a commercial contact cleaning product to clean accessible connectors and slots, both for memory and for the adapter itself. If you have recently installed a memory upgrade on the adapter, remove it temporarily to see if the problem disappears.

Text is scrambled, incomplete, or appears in an odd font

If this occurs when you build or upgrade a system, the most likely cause is incorrect video drivers. Download and install the most recent stable video drivers for your adapter. If it occurs on a system that had been working correctly, there are several possible causes. If text entered in an application appears in a strange font, but menus and other system fonts are correct, use preferences or options within the application to choose another font. If menus are scrambled only within one application, uninstall and then reinstall that application. If the problem occurs in multiple applications and system applets, system font files may have been corrupted or replaced with older, incompatible versions. The easiest cure is to reinstall the operating system, using its repair option. If you run Windows 9X, the hardware acceleration setting may be too high. Decrease it, as described in the preceding section on Windows 98/Me. Although this problem usually is obvious when the system is first brought up, we have seen it occur on a system that had been running perfectly at the highest setting. In that case, installing a DVD drive broke the system. As it turned out, reducing hardware acceleration by one level allowed the video card and DVD drive to coexist, but we ultimately replaced the video card with a later model that would run with full hardware acceleration.

Under Windows NT 4, you replace a PCI video card with an AGP card, and another card stops working

Windows NT does not support AGP, but treats an AGP card as a PCI card. If the motherboard maps the IRQ assigned to the AGP slot to the same IRQ used by the first PCI slot, installing the AGP card creates an IRQ conflict. Move the affected PCI card to a different slot, or use BIOS Setup to remap IRQ assignments.

Video is usually fine, but becomes jerky during DVD playback

This is often caused by insufficient system resources (such as a slow processor, aging video adapter, inadequate memory), by having too many other programs running, or by attempting to display DVD video at too high a resolution and/or color depth. If you use software MPEG decoding, rather than replacing the processor, consider upgrading to a video card that has DVD hardware support. If the DVD drive is ATAPI, configure it for DMA mode rather than PIO mode (see Chapter 12). Finally, Windows 9X IRQ Steering may configure the video card to share an IRQ with another card, such as a network card. Use Device Manager to check IRQ assignments and verify that the video card is not sharing its IRQ. If so, relocate the PCI card to a different slot.

When using an overlay DVD MPEG decoder card, one particular color (often magenta) doesn't display properly

This is an artifact of how some DVD MPEG decoder cards function, mapping the DVD video to one particular overlay color. As a temporary fix, connect the monitor directly to the video card except when you are displaying DVD video. The only real fix is to replace the DVD decoder with one that does not do such mapping.