Quite a few problems guys, advice please :)

[Duffydude]

My homebuild is now a year old and after setting it to sleep last week it wouldn't reboot. If I turned the power off at the mains and then on again, after pressing the power button the mobo would briefly light up and the fans would spin for a second before nothing again. There was no light on the mobo normally but there were lights on the GPU so I tried switching and removing RAM, checking all cables and resetting the CMOS and reseating the clock battery with no change in luck.
Then yesterday I borrowed a mates PSU and powered it up without connecting the peripherals, there was a strange high pitched sound coming from the PSU but the system seemed start up properly again.. HOORAY! Or so I thought, I turned the PC off again to connect the monitor etc to fully make sure everything was OK but the computer wouldn't start. The same high pitches noise was there and there were no lights on the GPU now and the computer won't even temporarily boot up like before. I thought if I put my old PSU back in it might return to its prior state of gpu lights and a temp start but its completely dead now nothing happens and now my PSU is emitting a high pitched noise when power is on just like the other PSU
What could have happened? Any help is greatly appreciated

Specs: Intel i5 2500k 3.1Ghz (ocd to 4.8), Nvidia geforce gtx 560Ti, 8Gb ddr3, gigabyte GAz68xud3pb3

 

[o1die]

Sure it's the power supply fan? It could be a case or video card fan. Is the cpu fan turning? First item is to remove the motherboard battery with the power supply unplugged. Then try posting. Your overclock may have failed suddenly. Hopefully your cpu still works.

 

[Duffydude]

After I first connected the other PSU, the computer seemed to boot up fine, all fans etc on at first suggesting my PSU was the problen. But now the pc does nothing at all, no lights and no fans. Do you mean boot it up completely without the mobo battery, or just reseat it again?

 

[o1die]

Reset the bios by removing the board battery with the power supply unplugged, then reinstall it. Then reboot. All you're doing is resetting the bios settings. Do this anytime you change a bios setting and the board won't post.

 

[Duffydude]

I've already tried doing what you are saying already though, to no avail. The 2nd time I tried it there now the only difference was when the power light on the GPU lit up briefly. Also if it helps any the PSU starts squealing when power goes through it and if I press the power button in the PC or hold it the noise dulls and then on release it loudens again.