No display signal from new PC

[Profiterole]

Hey, I've recently started building a new PC, and after putting everything in and wiring it up, I turn it on and there is no signal to the monitor. Also after 20 seconds or so of being on, the computer cuts out and restarts itself. I've double checked all the wiring and the only thing that seems loose is the 24-pin connector which I'm worried about forcing in all the way for fear of breaking the motherboard. Is this connection the problem or is there something else?

 

[Profiterole]

Do you definitely think it's the connector that's causing the problem then? All the parts are brand new so I'm pretty sure it's nothing to do with them being faulty.