More info needed on the problem to give you a more accurate analysis however, random reboots indicate a 'power' related problem and more commonly caused by a faulty or inadequate Power Supply Unit. Faulty or overheating CPU is another common culprit but...you mentioned the system booting to a Blue Screen and then rebooting at the moment and this behavior repeating in a cycle leads me to believe a software problem, a corrupt or incorrect device driver to me exact, though, as the other fellow mentioned, could be caused by a faulty CPU or RAM.

The million $ question -as usual- is: What has changed?
Wrong answer: Nothing, then there is no problemeither.
Correct answer: he added more Ram or something was installed/uninstalled or drivers for the X device was updated or the night before this happened electricity went out all of a sudden, etc.

~TL