My Windows 7 Ultimate PC suddenly starts crashing as soon as I log in using my password. For some strange reason my PC goes through the BIOS with no problems, gets to the log in screen, starts to load programmes as usual and then suddenly crashes with the error messages "no video input" followed by "entering sleep mode". It then appears to shut down, but there is a light still on the front panel but the only way I can get it to start up again is to unplug it from the mains.
Neither the main switch or the reset button will work. I am just going round in circles at the moment. Does anyone have any suggestions.