My computer is having boot problems after replacing psu

[I need help with my pc]

Hi, I just replaced my psu and gpu, but when i try to boot it up it says no devices detected or found(im on a desktop by the way) and its really screwing me over, ive checked the cables and put quite a bit of force. Anybody know why this happens? All advise is taken thank you in advance :/

 

[Lutfij]

Please follow this guide and see if you make any progress. Can you please pass on your full systems specs(include your OS as well)? It looks like your system isn't receiving optimal power. While on your older setup but new PSU are you able to boot into OS?