|To get to the command prompt tap F8 continuously after powering on. On the list it should show the Command Prompt options, although I'm not sure what you have in mind to do there.|
There is one simple thing you could try which occasionally helps get you out of cycling. Turn off the computer and disconnect from domestic power. If it's a laptop remove the battery too. Finally hold the Power4 Off/On button in for about 20 seconds, then reassemble and hope.
Are you saying it restarts when you are looking at the BIOS screen? If so it might be an overheating problem. Best hold off wiping the computer for now until you are sure it is not a hardware fault.
Always pop back and let us know the outcome - thanks