Static and freezing

I am using a Windows 7 64-bit, HP desktop computer. My video card is an ATI Radeon X1300 with 256mb. Out of random, my screen began turning black, freezing, and static appears at random places. I tried two different computer monitors, so my monitor is not the issue. The graphics card is updated along with Windows Update. I ran a virus scan and spyware; those came clean. How do I fix this problem?

Screenshot of a message appearing: