I wasn't sure to put this on overclocking or PSU so I just put it here. I built my computer about 6 months ago and it is great http://pcpartpicker.com/user/ThePCNoob2/saved/2Vpa
However whenver I try to overclock more than around 7% my games crash around every 30 minutes, is this is a power supply problem or is there too much heat being generated?
its more likely instability in your overclock, if it was your powersupply your system would just shut off.
I agree with webuelist, what are you using to overclock?, I would try running furmarks, for an exstended period of time and you can monitor temps and usage, see if there's any patten when or if it shuts off
Could it be fixed by getting better cooling or is it just a thing with the radeon 290x
Im using catalyst control center
If the temps are really high 85 degrees plus, them Mabey that's the problem
Yes and No, making something cooler can increase stability, and overclocking head room. But sometimes you have just reached the limit of what you can get stable when Overclocking.
Overclocking without knowing temps of cpu and gpu are just plain wrong. Second not every chip will overclock good.
That being said, no power is not the issue your system will not reach 600watt even with the oc.