You may also want to try disabling the hybernation support in the power options. I've seen that cause odd shutdown/restart issues with Windows XP.
If you are getting hardware diagnostic codes and machine check codes, this is all occuring outside the OS environment, before the OS even boots....
The ABCD lights on the back are diagnostic indicators, when you boot the system they will cycle through a sequence of codes and eventually go to...
Velva no :signs113
As I always say... When in doubt, buy both ;)
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