1>UPDATE your graphic card drivers from the ati radeon website by choosing your graphic card model there..
2>try updating the bios from ypur motherboard websit...
3>try cleaning your graphic card by a air blower,because dust on it may cause overheating of graphic card...
4>try playing your games with the side panel of your cpu open,,try it out also...
5>go to the system devices in manage option of my computer and do the PCI STANDARD TO PCI BRIDGE thing,,,,it might work for you
am sure any one of the above options would work for you..........