Test the Ram.
Run this to test it: http://hcidesign.com/memtest/
If you have 8gb of Ram, run 4 copies each with 2048Mb.
Next, uninstall and reinstall graphics drivers, direct X, do a windows update and do a run of CCleaner (Both cleanup and registry fix.)
CCleaner: http://www.piriform.com/ccleaner
Direct X 9 Redist: http://www.microsoft.com/en-au/download/details.aspx?id=8109
If you have an AMD Radeon Graphics card: http://sites.amd.com/us/game/downloads/Pages/downloads.aspx
If you have an nVidia Geforce Graphics card: http://www.nvidia.com/Download/index.aspx?lang=en-us
Download Coretemp and watch those temperatures, if they are exceeding 60'C on an AMD CPU, then it's to high, AMD's whitepapers have for the last several generations stated 61'c should be your maximum.
http://www.alcpu.com/CoreTemp/
(Please note that AMD CPU's have a temperature bug, add a 13'C offset because of it.)
Even if temperatures get high, then you shouldn't have any worries even if it hits 70-80'C, the PC should still run, just thermal throttle.
Finally, has your hard drive been clicking? Do you have an OCZ Vertex SSD? What brand and wattage is your power supply? What graphics card do you have? (Some brands of cards had dodgy paste, which could cause a GPU failure.)
What's your idle GPU temperatures, have you tried manually setting your graphics card fan speed to maximum before launching anything?