85c for the 2600k CPU? It's not PSU issue then (for now atleast). Your cooler is badly installed, it's broken, or someone has failed in applying thermal paste right! Over 70c for 2600k is dangerous! You need to remove the cooler, clean up the old thermal paste and re-apply a thin layer of thermal paste. Otherwise you risk destroying the 2600k completely!

u could also remove the CPU-cooler and install a better custom one if u are running on stock CPU-cooler.

EDIT: reading further about 2600k, it doesnt seem to have problems running at upto 95c-105c with TJ Max, though recommended temp is still under 80c mark for maximum stability and lifespan. So it might still be the PSU-issue. Would recommend getting a better cooler though, the stock coolers are awful.

Or the fan isn't pluged in, I did that once... 

Ah rookie mistakes, of course I had just swaped the fan out (to use on another system) and never plugged in the small one I left in there as the system as it wasn't going to be used. But still my fault, oh well.

Of course that system had an old AMD so it just kept going until it burnt out. Lucky all modern CPUs have a cutoff when they get to hot.

Oh or a busted heat sensor, had one of those once but that isn't very common. 

That is way too high for CPU temperature !

You have to check whether or not the CPU fan is working correctly, although I still think it might be a problem with the thermal paste. I imagine they just used the low cost paste that was on the cooler instead of applying a layer of quality stuff on the CPU. That would explain rather well why the problem started to show ~a month after you got the PC.

Oooh, that's not good. You don't want over 70 at max load ideally. You might need to be a new CPU cooler or re-fit or re-paste your current one.

I got the software to monitor it - not sure how reliable. Speedfan, but some reviews said it was okay enough to give the picture. And the temperature varied between 75-85 and the CPU usage during those temperatures was less than 1%, so it was just the computer turned on.. Not good at all.

That is not good at all, run any CPU intensive program and temps could hit 100. You might need to buy a new CPU fan and possibly some case fans for increased air flow. Luckily, like the PSU, all these bits are pretty cheap. Try refitting the CPU fan and re-applying thermal paste which you can easily find on the internet, check the RPM of the fan in Speedfan too. Try checking temps with realtemp or HWMonitor too just incase Speedfan isn't accurate.

That's a huge tell right there indicating an improperly seated heatsink. Those are 100% load temps, not 1% idle temps. 

Remove, clean, reapply fresh TIM and reseat. 

Also, check if your fans are working properly. Connected properly? Mounted in the right direction? Spinning at the appropriate speeds?

Your power supply may actually be fine. The factory heatsink should be fine as well assuming factory clock speeds. So before you start buying and replacing parts, buy some decent quality TIM and reseat the heatsink.

Once you have your temps under control, and have verified with load tests using something like Prime95, you'll know if your PSU is cutting out on max draw with your current hardware set up.

Also, check the task manager to see what background processes are running. There are bits of code that run unnoticed in the background that can increase CPU temps even at idle. Some malicious, and others just not coded properly.

^

He's right, it might not actually be the PSU, could be the CPU overheating.

Like he said, re-seat the cooler and re-apply the paste, check cables to the fans and make sure no other cables obstruct the fans. Check the fan RPM and CPU temps using Speedfan and other software like HWMonitor and Realtemp. Run Prime95 and check temps again.

Do you have a multimeter? I would check to make sure the PSU is getting voltage. Second, I doubt this is the case, but I would try something in the outlet to ensure it works since it won't turn on at all. I mean it is a very slim chance, but sometimes its things you wouldn't expect to be a problem.

I've ordered some thermopaste, will reapply it once it arrives. All the fans seem to be working fine, I've opened the side and turned on to check, almost caught my finger in the CPU fan, gg me. But the actual case has about 4 additional fans too.. So I think it's most likely the thermopaste, see if that will have positive effect, thanks for the advice guys. If the problem persists I will likely send it off to them to see if they can pinpoint anything in particular, and they will have to fix it I guess.