Fans start to spin then stop, one beep from Mobo

[gibbynator]

Alright so I have been futzing with this for awhile. I was testing a PSU for someone and it worked, pc started up fine. Reinstalled my PSU and now wont start. The fans start to spin and I get one beep from the mobo the first time I press power. Nothing will happen if I press power after that unless I flip the psu switch off and on.

OS: WIN 7
Cpu:i5 4690k
Mobo:MSI Z97 G55 SLI
Gpu: GTX strix 970
Ram: team dark 8gb (X 2)
Psu: corsair cx 750m


I have tried redoing the wires for the mobo that I had to take out for the PSU (CPU 8pin, mobo power, gpu 8pin). Any ideas?

 

[Ralston18]

Update your post to include full hardware specs and OS.

Motherboard: make and model? Motherboard's User Guide/Manual should provide the meaning of that one beep (short, long)?