Obviously give a different mouse or port (preferrably both) a try first. If that doesnt help go here and download both programs:
http://www.techpowerup.com/atitool/
http://www.mersenne.org/freesoft/#newusers
You don't actually have to create an account to use Prime95, you should be able to just run it in place. Run the first seperate (atitool) and then both together for about 15 minutes or so and the two ought to tell you whether its on your graphics card or if its a power issue.