Two days ago while sitting at the computer, I heard an intense electrical bang. It remininded me vaguely of a capacitor or voltage regulator exploding (both of which I've experienced before). Naturally, I stopped everything I was doing and went out in search of the problem.
No smells. No smoke. The computers and all nearby electrical appliances seemed to be running smoothly without interruption. But later that night my computer spontaneously rebooted. On restart it became apparent that the video wouldn't work except in VGA mode. Uh oh.
At the time, I had a pending software update on the go (iTunes) so I started looking for a software problem with a newly installed system service. Ahh, bingo. The event log says it's having trouble loading the GearASPI driver and there are reports of that causing system startup problems. Ok so I manually uninstall it. Hmm... still doesn't work except in VGA mode. As expected, reinstalling the video driver accomplished nothing.
Looks like a hardware problem. (Gee, I wonder what that bag was about earlier?) So I put a new video card on order for testing purposes. The current card, a eVGA GeForce 6600, had been giving me problems anyways. Meanwhile since I can still remote desktop into the machine, I leave it alone. Bad move.
This morning the machine locked up again. So I finally open it up and take a peek. After removing the video card I notice it has 3 blown electrolytic capacitors on the board. Yikes! Fortunately nothing else was damaged.
Morals: 1. Trust your first instincts. 2. Open up the damn machine as soon as you suspect it's a hardware problem. 3. Don't dismiss loud unexplained noises!