this could be a bios problem - have you looked at the version number of yours versus that on the makers site? I had 1 pc with the problems you describe. This has not reoccurred since flashing the bios with the latest version and upgrading to Windows 7. I do not know which of the two things cured it but I did the bios first and used the pc for about two weeks before upgrading from XP and the failure to start did not occur. My failure to start was approximately after about thirty reboots.