It hasn't been like this forever, but I'll give some examples.
I'm playing the Sims 2. You know the sound your computer makes when is it loading and crap? Well sometimes it makes the sound and does good, but sometimes instead of loading something, it restarts instead!
The other day after downloading the WoW beta for the 4th time, it crashes midway through installation, for the 4th time.
I have about 7 Foxfire windows open. I close them all, and after closing the last window, I get a restart.
It happens everytime I quit a game also. When the game shuts down, the desktop is shown for a fraction of a second then it shuts off. Then I have to keep the computer OFF for about 5 minutes before I can turn it back on. If I don't, as soon as it boots up it restarts again.