CPU not booting! Fans spin, green led on.

[Drummingknifes]

My PC won't start up. The fans spin, and the green led on the motherboard lights up. The led in the power button of my case stays off. No boot afterwards, neither the mouse or keyboard receive power either.
I'm kind of desperate everything was fine a while ago.
I opened up my PC to apply new thermal paste to my CPU, afterwards I applied some compressed air for general cleaning. I closed it up, tried to boot but no luck.
Some specs:
CPU: Intel i5 3340
GPU: Asus GT 440 (about to upgrade to Gtx 750)
MoBo: Asus H61 M-E
Psu: cooler master extreme power plus 600W.
As a side note, do you think the gtx 750 will run well on that psu? (Assuming everything works fine in this frustrating scenario).

 

[i7Baby]

The PSU is pretty poor quality but should run the gtx750 OK.

Disconnect your OS drive, fit a PC internal speaker per your mobo manual and post the post/beep code that you get per http://www.computerhope.com/beep.htm. You'll have to look in your motherboard manual to see what type of bios you have eg ami or ibm.

 

[dlist]

This happened to me awile ago, turns out the 24 pin power cable came loose. Check all your cables, specifically ones going onto the motherboard.