XP in restart loop

[DKane]

I was just browsing the internet when my PC suddenly decided to restart. It got to the XP loading screen then crashed and restarted again. It does this indefinitely. It doesn't shut off or anything just gets to the XP load screen then restarts and I get to choose between Safe Mode Last good configuration etc. I can't get anything to work. I don't have the XP disc. From what I've found it seems hardware failure is likely but how I can I find out what the problem component is if that's the case?

Thanks

edit: I was able to turn off 'automatic restart upon failure' and got the blue screen error. Not sure if this would be useful but it says

IRQL_NOT_LESS_OR_EQUAL

and also

*** STOP: 0x0000000A (0x00000000, 0x0000001c, 0x00000001, 0x804FB006)

[glc]

http://support.microsoft.com/kb/314063

I'd start by testing the ram.

www.memtest.org

I don't have the XP disc.

This is going to be very inconvenient.