Question Desktop refuses to turn on

Mar 1, 2019

I'm currently helping a mate fix his desktop however no matter what we have tried it doesn't work,

The problem first started when the computer overheated, my mate gave me a call and I went to have a look, after it was completely cooled down I pressed the power button and it lit up, however the fans wouldn't start up, computer wouldn't post, no sign of any activity but all the lights on the panel and board were working, the HDD light also was just a solid light. I've tried reseating everything and that hasn't worked, running it just off the minimal parts didn't do anything either, I was grounded whilst handling it to avoid static. Did a Bios reset, still nothing. Thinking it was the motherboard, I replaced the motherboard with an identical one that I tested to work in another setup however putting it in this just did the same thing. I've got no idea what it could be. Also on both occasions, no beeping or any form of error codes.

Specs. (It's a very cheap build)
Motherboard: Asus P7P55 LX 1156
GPU: Asus one that came with it
CPU: I5-750 Lynnfield.
PSU: some offbrand PSU, rated 750 watt. Tested on other systems to check if it worked.

Help is much appreciated.