Computer won't turn on

[Pyrofunto]

Hey guys, I have been using my PC for some time now and everything was fine. Today I finished installing a custom watercooling on it and it went start... if I jump the psu it works but if I connect the MB it doesn't start. 

 

I have checked the front panel connectors, and there is light on the LAN connector so I guess the MB works so I don't understand a thing right now....

 

Setup:

MSI Z270 SLI PLUS

GTX 1080

I7 7700K

Bequiet 650W

32G ram

 

 

Ps: 

It is a full hardline watercooling so removing something is a real hassle 

[Pyrofunto]

I think either the MB or the CPU is dead but is there any way of knowing witch one without having access to known working pieces?