Most likely a gpu driver errors or memory.
Have you ran Memtest86+?
There's a possibilty one of your ram module might be defective.
Run Memtest86+ one stick at a time to isolate a bad module.
Use the mobo default ram settings and run it for a reasonable amount of time.
At least 30min-1hr for each module.http://www.memtest.org/
If your ram isn't the problem it's probably improper settings on your overclock.
Have you ran any stability programs like Prime95 for your oc?
An underpowered psu would run hot and the fan would be noticeably loud.