System Lock-Up/"Crash" (Unexplained)

[DepthsOfRlyeh]

I had something bizarre happen that I've never had happen on any of my systems, so I'm trying to figure out what happened. I'll try to make this short but detailed.

- Playing Left 4 Dead
- Crashed to desktop/Steam still up and L4D minimized to taskbar
- Entire screen flashing on/off with pink broken-up lines (sort like what happens with a GPU crash from heat etc.), then began flashing on-and-off entirely (as if monitor shutting off)
- LED's on my RAM had three sections or so that went blank, but LED's above/below were solid but not moving (don't believe RAM was the problem, however, it was just a result of what ever happened)
- Could not do anything on desktop what-so-ever

Had Everest open so was able to see temps in-between screen blanking-out and temps were fine. Nothing too hot (mobo 32C, GPU 65C etc). Had to hard shut down.

Nothing in Event Viewer, no driver error... nothing.

Went back and pushed system hard with L4D and it was fine.

Usually something such as this is a display driver or hardware problem, and/or something set-off by a game, but there was no error and my system is in good shape. I've never had anything exactly like this happen before. All hardware relatively new, listed below.

Any ideas?
Much appreciated.

System:
ASUS Rampage Formula (nothing OC'd)
E8600 (stock)
2GB Corsair XMS2
Corsair HX620
GTX 280 (stock)