|Try F5, also re-try F8 a few times as you may just be pressing it at the wrong moment. If you have a USB keyboard, and your system has a PS2 port, try borrowing a PS2 keyboard.|
CCleaner won't run in DOS but it will run in safe mode, though it won't help. You need to 'disable restart on system failure' and see what the blue-screen message you get says.
"I've always been mad, I know I've been mad, like the most of us..."