Computer Woes

[sailorzeo]

Every so often, my computer shuts itself down, doing a good imitation of a British police siren. We've replaced the power supply, done some other work on the box, and still it does that. It did it last night while I was playing Sims2, just as two of my girls were going into labor. :-P

So does anyone know why my computer shuts off and screams at me, and what to do about it?