What can cause my PC to hard lock on a windows SS after ~5 mins?

[FluxCap]

The only changes I have made to my system in 2 months are refresh rate up to 75 and new catalyst 3.4 drivers instead of 3.2s. That was a week ago and this started yesterday. I have to do a 5 second power off on the button to get it shut down. Any ideas?

 

[FluxCap]

I changed the cats back to 3.2 and a lower refresh and even another windows screensaver and it still does it. What could this be?