Yesterday morning I shut down my computer as normal and when I came back I switched the computer on and my AMW Screen was blurry and shaking at the screen to type the password in. I switched off at mains power and then for 6 hours after trying to reboot 30 times, the Fan instead of staying on for 5 seconds and then going quiet was staying on for about 30 seconds before going quiet and there was no beeps and the Hard Drive was not kicking in. I removed mouse, keyboard and all other USB devices and unplugged the Hard Drive and unplugged most things connected to the Motherboard and reconected them and tried to reboot with just the power supply on but no change. I then cleaned the Fan and removed the build up of dusk but still no change. I left the computer off for about 1 hour and then it booted as normal. Computer is as normal today. Does anybody know what would have caused that problem yesterday?