When I uninstalled PCanywhere from our Windows 2000 Server (Dell Poweredge 2600 Tower) at work, my display adapter stopped working (i.e. I could only display in 16 colors and at limited resolution).
My first attempt at troubleshooting was to buy a PCI video, card and install it, but that still didn't work. Whether it was the onboard video, or the new video card, it kept giving me "Code 31" errors when I clicked the device properties in the device manager.
I kept hunting around on the web, and this is what finally led me to a solution:
http://support.microsoft.com/kb/270008
Even though this link is about CD-ROM devices, the problem was the same for me and my display adapter trouble. In the registry key [HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlClass{4D36E968-E325-11CE-BFC1-08002BE10318}] there was an entry called "UpperFilters" that was set to "aw_host." It turns out this was left over from PCanywhere (found that out by Googling "aw_host.") I deleted that registry entry, and now my video works again! (high color, higher resolution display settings work now.)
I haven't tried the regular on-board video, but it probably still works too.