Possible Overheat / Black Screen issue

I'll do my best to post my specs here:

64 bit - windows 7
intel i5 2500 @3.30 gHz
8.00 Gb ram
gtx 570
m12 bronze seaonsonic 620w power supply


I have had an increasing issues with what seems to be over heating issues. The system is almost 4/5 months old now. When I first purchased it, I ran rift on ultra, with 0 lag no problem. As of the past couple months, Medium graphics on various games became an issue. I never monitored the system's temperature when everything was running smoothly, but core temps are reaching 60 degrees in the summer.

The issue essentially is, randomly during gaming, the monitor goes to sleep and all the fans of my computer start spinning super loud. This occurs whenever I play the gw2 or the secret world beta. In fact, I can hardly even play rift on high graphics now without black screening every couple hours.

A solution that has come to my attention is that, since I got new hardware, I did not reformat my system completely. I simply reused my old hard-drive. I understand there could be some systems compatibility issues. I just wanted to get the communities opinion before I reformat. Please I'd appreciate any other alternate solutions, I want to avoid damaging my system as much as possible.