It could be your motherboard or cpu. While rather drastic and slow, try disabeling your onboard cache and run it hat way as long as you vcan stand it. Next try your cpu cache. If those don't work remove the "enum" key from your regestry, remove all cards but the video, and install one at a time. restart after each one and often.
Use the computer after each install to try to find the culpret. Allways check the DEVICE MANAGER FOR CONFLICTS OR PROBLEMS