PC won't turn on after first boot.

it may be a mb bios glitch. try using the usb flash back and put the newest bios code on the mb by the usb flashback port.
download the 1805 bios and rename is z77st.cap if the mb wont post look at the mb for any fault led. most asus mb wont post if they think there an issue with the cpu fan. you may have to clear the cmos or press mem ok to get the system to post again if it a bios glitch.

Thankyou for your reply

Okay so i got the USB flash drive with the correct bios on it, z77st.cap (not easy when the only other computer you have is a MAC that doesn't want to run any windows files) However nothing happens with i press the bios button.

I have reconnected all the wires re-installed the ram / CPU. checked there was no damage to the pins, tried turning it on with only the MB/CPU/RAM connected and nothing has worked.

There is a constant yellow LED on (which is the power standby light) when i connect up the power so i know it's not the PSU and that the MB does recognise is has been give power but nothing else whatso ever will turn on.

The MB also say it has other smaller LEDs that flash when something is not connected or working as intended, Non of these are flashing.

I held down the Bios button for a few seconds, and it started flashing, whereas before i just pressed it. so thats good but it hasn't made it work.

The i connected a headset to the front USB port and it powered up the headset. It's so annoying i can't think of anything else to try! It clearly has power, everything is connected, nothing is visibly broke and it's already been successfully booted once.

Any ideas ?

the usb flashback port is the bottom usb 2.0 port under the ethernet port it has the white writing on it. if the mb wont post after an bios update try clearing the cmos.

Clearing the CMOS worked!, i almost through the little cap away thought because i thought it was just a protective covering. Thank god i didn't.

Thankyou Smorizio you saved my so much stress, thankyou, thankyou, thankyou.