Magister,
I'm a fairly inexperienced user, so I wanted to clarify some of the steps you made to correct your problem. First off, I have a Dell XPS (2 yrs old) P4 _GHz with an ATI 9800 128 MB. I also had ATI's Catalyst already installed, and everything seemed to be working fine. I didn't get Max Payne, but I did just get Doom 3 a few days ago (only $20 now). The installation (including the latest patch update) went fine, and I played it without any problems. The next morning, however, my monitor was blank/black. I could see everything on my desktop, but only after turning the monitor off and on; and it would last for only a few seconds.
I also noticed that there's an "ATI 9800 Secondary" when I checked my display driver. My computer was also registering a "New Hardware" USB connection, which was odd, since all my peripherals were accounted for.
I ran SystemWorks (no help)
Uninstalled Doom 3 (didn't fix it)
Couldn't remember if I had first installed Net Framework, so did that again (actually resolved problem, but back to same problem later that night)
Uninstalled ATI control panel then display driver (in that order), uninstalled Catalyst 5.9; then reinstalled Catalyst 5.9 (no help).
So here I am. Regarding your own steps, when you say "Get out your AGP chipset drivers," did't you just uninstall them? Or do you mean literally readjusting the card in that slot? And how do you run Dxdiag? Is that in the menu after selecting F2 on rebooting?
Thanks for your help in advance, and for anyone else's out there.
Drewhead x)