Year old gaming PC having won't power up

[Legateblake]

Hello overclockerz friends, last year you guys helped me build an amazing gaming pc that I've been having so much fun with. That post can be found here: http://www.overclockers.com/forums/showthread.php/740660-New-Gaming-Computer-around-2000-budget

My current setup is very similar to: http://pcpartpicker.com/p/nB9qmG
only differences are the CPU cooler, corsair vengeance RAM instead, and a QNIX monitor

For the past month my PC has been having some problems booting. It seems to randomly choose when it wants to power up. The first time it happened I clicked the power button and nothing happened. I figured one of my power cords was slightly unplugged or the wall outlet might have been the problem but I messed with the cords and changed outlets and nothing changed. I had some classes to get to so I left for those and came back around 9 hours later and was prepared to take it apart and see what was wrong but it started immediately this time so I wasn't complaining. Then my computer has selectively done nothing when I've tried to power it off since then. Its gone as far as a week with no problems then I'd turn it off and forget something and try to start it back up and it wouldn't power up. I've tried several things to fix this, including taking it apart and testing components, checking the front case power wiring, tested a new power supply thinking for sure that had to be the problem since the motherboard light came on but it didn't seem to be getting power.

I'm only moderately knowledgeable when it comes to computers but I've built quite a few and have never had a problem I couldn't fix on my own. This sort of selective error really has been throwing me off, usually I would just turn off the power supply and unplug it from the wall for a few hours hoping it would work fine but since I've replaced my power supply I can't get it to power up again. (also forgot to mention my motherboard has a directkey that sends it straight into BIOS so I don't think it's a problem with the front power button)

My only thought is that my motherboard needs to be replaced (possibly a short?) but would really love to hear what you guys think of my situation.
Thanks for your time

edit (just realized typo in the title *facepalm*)

 

[ATMINSIDE]

I'd build the system outside the case (on top of the motherboard box works well) and see if the issue persists.

 

[Legateblake]

Okay, this problem was a weird one. After buying a replacement power supply which didn't fix the problem, I replaced my motherboard still seeing no change. I gave up and took it to my friend that owns a repair shop to take a look at. He tested quite a few things determining that the new power supply was dead, no big deal I've had dead parts before. I sent it back and received a new one which I installed into my system and it also didn't work. I tested it with a psu tester which showed it was dead as well. I new then it was a problem on my end and I looked through everything to find out what was shorting my system. The culprit was a recycled hard drive from a laptop that was unrepairable while under warranty so they gave me a full refund and shipped my hard drive back to me. I installed it with my ssd without really checking the quality of the hard drive after shipping. The pins on the hard drive were bent/broken in places so it was not making a good connection with the psu causing these shorts. So a tip from a very failed troubleshooter, be careful with recycling old parts and beware of faulty shipping =/. Hopefully this update will help some people never make the same mistakes as I did, also I spent around $300 on replacement parts trying to fix my system which I'll probably put into building a pc for my brother. Have a nice day

 

[ATMINSIDE]

This is why I suggested building outside the case, with minimal equipment connected...

If you'd done that, you would have seen that having a device disconnected let the system boot properly.
Then you could have connected one by one to see what caused the issue.

 

[Legateblake]

I did try building it outside of my case but my psu didn't work with the bare minimum on my mobo since it had shorted.

 

[ATMINSIDE]

I did try building it outside of my case but my psu didn't work with the bare minimum on my mobo since it had shorted.

Bare minimum would be CPU, motherboard, 1 DIMM, and using onboard GPU; just to see if you can get it to power up and POST.