[H] Strange problem

[Thane Sherrington (S)]

I've got a computer that turns itself off suddenly (as if the power 
cord was pulled) when playing Myth 3 or Max Payne 1.  It plays UT2004 
and Q3A fine.  It's running XP Home with all updates, an ATI X550 
video card, AMD 3500+ on an MSI Neo-4 (NForce 4) motherboard.  I know 
Myth 3 and Max Payne 1 are not written for XP, but I was wondering if 
anyone has seen this before.

T