Black Screen of Death

[Grit]

To check if your card is overheating, run MSI afterburner (or something similar) in the background and see where the temperature peaks.. before you "black screen"

You still haven't described your issue properly. I asked if your computer is restarting, or shutting down completely, or giving you an actual error screen before rebooting. It may only take a few minutes for a card to overheat.

Your computer is compatible with 64-bit, but that doesn't necessarily mean that downgrading won't help. You should also try turning off sleep mode, as someone else recommended.