Computer turns off a few seconds after turning on, then is normal.

I'm not too familiar with the i5 2500k, but I'm pretty sure your OC is waaaayyyy to much. Isn't it normally 3.3GHz? I did some looking around on google and kept seeing people worried about setting their 2500k to 3.8GHz at 1.4V. It's not very safe to go over 1.4v, so I'm thinking your problem lies with the CPU not getting enough power for that clock speed. How much do you know about overclocking? You're really supposed to go up in small increments until you get a failure, you're definitely encountering a failure, so start with modifying that. You've increased it by 1.2 GHz, that's almost a 25% increase, I usually get stable OC's with only a 10-15% increase.

I'm assuming your purchased your GPU factory overclocked? Generally you should never OC a card that has already been clocked because for the most part, that card is already stressed as it is. Again, since you didn't modify the voltages (which you shouldn't mess with much anyways) it's not getting the power it needs. Basically, you telling your CPU and GPU to work harder with the same amount of energy input. I'd reset your video card back to the factory OC.

The 2500k is unlocked "k" so people have gotten stable 5GHz clocks, I think it may be the voltage. And as for the GPU it could be that but I've also heard of people OCing it to 850MHz and some 900MHz. So I think the problem may lie within the CPU voltage.

I have a Corsair HX850 850w PSU, so plenty of juice but idk about the idle thing like you are talking about with your XFX PSU, maybe that could happen with this one too.

Okay thanks I really appreciate it. The problem may have diminished. My overclock seems fairly stable I can run all my games and they do not crash, I ran Prime95 for about an hour (probably not long enough) and nothing went wrong so it seems fine so far.

It sounds like you are having a cold boot.

If I'm reading this right, you push on the power button, it starts up, then about 10 seconds later, it shuts down, then it restarts itself just fine. Is that what is happening?

If so, do the following. I have also have a 4.5 OC and my cold boot started right after I OCed it. You don't say what your mobo is, but if you have 0301 version BIOS on an ASUS, go in to your BIOS and set your DRAM to XMP. Then, go to your PLL overvoltage and set it to disable. That fixed mine.

An ASUS rep that I emailed fixed mine for me with those suggestions and it worked. He said I will not even need PLL overvoltage until I get into an OC that's 4.7 or higher.

a 4.5ghz overclock is very stable and easy on the 2500k, with perfect temps using air cooling like a 212 Evo.

Hope this helps.

I actually have the same exact mobo as yourself unless yours is just the v version, mine is v-pro. But the problem seems to have gone away, but I'll take your suggestion anyways so it won't do this again. Thanks!