Rig shuts down after about three hours of mining

[previous]

I have the following set-up:

Corsair AX1200 1200W PSU
Asrock Extreme 4 MB
4GB RAM
3xSapphire Dual-X 7950 GPU
1xAsus DC2 7950 GPU

2 x16-x16 risers
2 x1-x16 powered risers

After first stable setup (no HW error, very few rejects), power from the wall was 1100V (OC and powertune). After 3 hours, the computer shut down. No error, no nothing, just shut down. I have decreased the clocks and disabled powertune. The power from the wall is about 900W. Still, about 3 hours after starting, it shut down again.

What can cause this? A faulty PSU? Can it be something else?

Thank you.

[wunch]

too much power draw or too much heat build up

[balanghai]

Hey you haven't mentioned your OS. Try running in Ubuntu or other Linux distro if the problem still happens, check your BIOS' temp shutdown, maybe it's quite low, you have to increase it to at least 90c.

[best-miner.com]

Check the logs for CPU/GPU to confirm whether it is because the temperatue, increase a bit, and if it still happens, try add a fan to cool may help a little too.