It’s a shot in the dark, but have you guys run msconfig and disabled all your startup items? It’s the easiest way to remove the possibility of 3rd party software causing issues, or least mostly remove the possibility.
If you don’t know how
click Start
For win7, click in the “search programs and files”/For WinXP, click Run
type in msconfig and hit enter
In the new window that comes up, click on startup, and uncheck every single box
Hit apply/OK and reboot
Try to run the game when your PC comes on, without running anything else at the same time.