I have recently been experiencing a lot of COMPUTER crashes im pretty sure it isnt caused by the software as it sometimes occours EVEN before windows has started to load or anything appears on the SCREEN but other times it works fine and dosnt crash at all. but it always takes about 10 crashes before i can get the computer to work properly. I have tested my memory with memtest86 and i think it is either the motherboard cpu or psu but am not certain is there anyway to test to find out which it is and also is there anything else which may cause it.Please Read This First - Viruses & Spyware

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When your problem first START? Perhaps you need to better maintain your PC:

Computer Cleaning Informationim pretty sure it isnt software problems becasue im using norton 2003 and AVG as anti virus and im also using adaware to stop any spyware plus i use a firewallIf you feel it is hardware related, read the article I posted..

Dust may have become an obstacle for your fans. It could be that they are not cooling properly and need to be cleaned.  more info on system....it could be the hard drive  failing or bad blocks on it ...or anything...when it crashes what do you get on the screen..