No display when PC is on, appears to be motherboard or PSU

[Sindenization]

A few months ago I had the same problem with my PC where it would turn on, but nothing would display. I moved it across the room, and changed the power cables, which cause it to work.

I now am having the same issue, but it is far worse. Upon testing, I have whitled it down to two things, my PSU or my Motherboard.

I was wondering what part is most likely to be causing the issue?

Along with that, why might it be causing the issue? (I.e. Not enough power, fluctuating power, shortages on the board, etc)

And finally, is there any cheap way to test which of the two parts it is?

Edit: It works out of the case, on a wooden table but not always.

I have moved around all the PSU 20 pin cables individually when it wasn't working and none of them made it display anything.
And display does not work on board or with my GPU.

 

[alceryes]

The 'free' (except for time spent) way to test would be to go to the store and 'borrow' (purchase and return after testing) a good power supply.

 

[Sindenization]

The 'free' (except for time spent) way to test would be to go to the store and 'borrow' (purchase and return after testing) a good power supply.

There's no stores around me that sell computer components, I'm in Europe, and have to get everything online. I could order one and return it, but would cost shipping and possibly a restocking fee.

With it now working out of the case, it's leading me to believe it's the motherboard that either doesn't like being vertical, or has something shorting at the back. Maybe that's weird

 

[alceryes]

It should turn on, every time.
When you say 'not always' that leads me to believe that you have a component failure.
Have you tried a minimal boot? CPU, 1 stick ram, no drives, onboard video only (if it has it)? This is just to see if you can get into BIOS and if it POSTs like this every time.

 

[Sindenization]

It should turn on, every time.
When you say 'not always' that leads me to believe that you have a component failure.
Have you tried a minimal boot? CPU, 1 stick ram, no drives, onboard video only (if it has it)? This is just to see if you can get into BIOS and if it POSTs like this every time.

Yes, it does turn on always, just doesn't always display.
Yeah, I have mainly been testing with minimal boot. THat's how I narrowed it down to the Mobo and PSU. I reseated the CPU yesterday too, and used a new stick of RAM. But still the problem did persist.

As it was working outside the case, but not in the case, all times except once, I have just placed some paper between the motherboard standoffs and the motherboard and screws, I'm now going to test this, as it is the only thing that changed between it being in the case and out of the case.
However, this doesn't make much sense to me as to why they would cause display error