For no apparent reason my Windows 7 Ultimate configuration keeps crashing at various stages of the boot process. Sometimes it crashes as soon as the BIOS starts to load, sometimes it will let me get into Safe Mode, sometimes it will let me try last kown good configurationand sometimes I can even get to the desktop for a few seconds. However it starts the computer then crashes and then the only way I can restart is to physically remove and replace the power supply cable. The on/off button will not work, restart does not work and whatever you do with the keyboard or mouse fails.
Does anyone have any suggestions as to what might be the problem and what I can try?