PC wont turn on

[Contana]

So the PC has become very problematic recently, although i have had the same problem throught the year since i bought it, but only occasionally. Basically, sometimes while idle, simply browsing the net or at half load the PC goes black screen, buzzing sound from speakers and freezes and sometimes then restarts or not at all, sometimes it just turns off instantly and when you try to turn it on it flashes PC case LED for half a sec, PSU turns on for about a half a second and turns off again and even when you unplug the PSU cable 30 times it wont turn on, sometimes a whole day, sometimes only 30 minutes... also maybe once in 2 months there's a BSOD about sync memory...
After 2 days of that ( recently, which is why i'm writing this ) i simply turned the PC on the side, and it turned on just fine and i have put it back in the vertical position and after 3 days it's running no problem, i have checked all the connections, there seems to be no shortage either ( that maybe a connector is touching another connector ), i just don't know what it is. I can only try reinstalling OS and reconnecting all the connections again ( Just this second it turned off again, just instantly, a total power off, luckily the browser saved this text )

CPU: i5 4500
GPU: GTX 760
HDD:1 tb WD blue
RAM: 8 gb 1600 mhz Corsair vengeance
MBO: H87 HD3
PSU: GS corsair 600 W

 

[theonerm2]

It sounds to me like your motherboard is dying.