Help No signal from pc monitor.

So here how it went.yesterday i brought a new mobo [N68C-GS FX] then i installed the mobo in my case i added ram,cpu,gpu,ide,psu and connected them to the motherboard then i switched it on and it did not even boot up so i took the mobo out of the case and booted it again this time it worked so i installed windows on it and decided to put the mobo back in its case the psu connectons to the mobo were tight when i was dissasembeling it and putting it back in the case then when everything was back in its case this time it booted in the case but there was no signal i tried taking the mobo out of the case again but still no signal so i am kinda stuck now and i need help