I tried Sampson's suggestion and it worked once. After I turned off computer and turned it on next day, same problem - blue screen w/nv4_disp infinite loop message.
Checked Sampson's settings and they were as set as recommended.
This is what I've done so far:
-Installed updated driver for nvidia GEForce FX 5200 card. System worked for about 7 hours, then blue screen, etc.
-Make changes to Display recommended in Sampson's post 12/28/05. System worked until I turned it off and then turned it on next day.
Incidentally, when I turned system off last night, it did the shutdown process until it got to the place where just the wallpaper was on the screen. I did a Ctrl Alt Del (task manager which came up) and then system shut down. I did not click End Now.
I have a Dell Desktop 4600 series running Windows XP home. All updates installed.
Suggestions on what I can do next are appreciated.

bad hardware ?