Overclock it a little bit at a time 0,1Ghz so start at 4Ghz without turning up the voltage. Then run Prime95 in CPU torture mode in 3-4 hours and see if it runs stable. Then you can try adding a extra 0.1Ghz and try again.
If your pc shuts down, crashes or if you can see its not stable, but the temps are fine. Then it's because it needs more voltage.
While you do this, use HWMonitor to check in a couple of times under the test, to see if your CPU gets too hot under these loads, if it does, you'll need a new cooler to go any higher.
I expect your cpu cooler won't be up for the task after a couple of these steps, especially since Haswell runs pretty hot compared to the old processors. Reason for that is some stuff from the motherboard now being built-in the processor on haswell.
Hope this helps!