Yeah, not a lot to go on here.
I will say that back when I had my 2500k in my main computer, with a P8Z68-V motherboard, I had it overclocked at 5Ghz and everything was stable but sleep was always quirky to the point where I simply left my computer on all of the time. I assumed that it was a side-effect of the overclock but never really cared enough to investigate further.
But what do you mean when you say that it won't shut down? Do you just mean that at the very end of the shutdown routine it simply sits at a black screen without actually turning off? I've had that happen on a few computers before also over the years. After a certain amount of time, it's okay to simply flip the switch on your PSU or hold your power button down for 4 seconds. The main purpose of "shutting down" is to close all in-progress operations first, and anything relevant would have closed by that point.