Re: GTx 280 pink screen crash on first running 3D game from 2-3 hours rest.
When something heats up it expands. You probably have a broken part. But when it heats up, it expands, finally pressing the slightly disconnected parts together. Then when it cools down and contracts, the broken area stops touching, and the problem repeats.
As you say, you have to turn the machine off for a couple of hours for it to happen again.