i7 3770K unstable overclock?

[BenTan]

Hi,

My PC has been freezing on occasion and am trying to figure out the problem. I'm currently using an i7 3770K at 4.5 Ghz, 1.3V. I'm also using Windows 8.1 Pro. The freezes are random and usually happen while web browsing and listening to music or when I leave it overnight. Temperatures are in the low to mid 30s on small load and when running a blend test, 60s to 70s. It's nothing major since it happens rarely and on occasion.

The first time I overclocked my CPU, I ran Prime95 on small FFTs for 24 hours without experiencing any crashes. Since then I haven't had any issues with freezing. Some of the changes I made after the overclock was the cooler (H100i) and the OS (Win 7 to 8.1)

I didn't encounter any issues until I went overseas for 3 months and came back. Before I started the computer for the first time since coming back, I changed the graphics card from a GTX 780 Ti to a GTX 980.

When I started experiencing freezes, I ran Prime95 again using blend and it crashed shortly after. So I upped the voltage to 1.33 and it ran P95 for 24 hours without crashing. But I still experienced random freezing.

What I did next was set the voltage back to 1.3V, remove the CPU block, cleaned out and reapplied thermal paste and reapplied the block. I ran P95 again but this time with small FFTs and it crashed within less than a minute. I upped the voltage to 1.35 and ran P95 again and the temperatures were in the 90s, a lot higher than during the first overclock. I have yet to test other voltages.

I'm just wondering how my overclock was stable the first time and now it's not. I haven't had any freezing or crashing during 6+ hour gaming sessions. Could the freezing be non CPU related? The motherboard is a Gigabyte GA-Z77X-D3H. Any help is greatly appreciated.

 

Thanks.