PC wont start - Cpu fan not running

So i was gaming on my pc and it randomly froze and my speakers started to make a weird noise so i turned off the pc asap. I tried turning it back on and it seemed like it was booting up and it would shut down again . it did this a few time so i decide to open up the case and see if there was something wrong. turns out the cpu fan wasnt running, it would run for less than a second and it would turn off as if something was constraining it from spinning. but there wasnt any cables or anything at all that could of cause it. i thought it could of been a fried cpu fan so i decided to try the same fan on another build i have and it works good , it spins as it should. i also checked the psu ,again i unplugged it and installed it into my other build and the psu didnt seem to have a problem at all. so now i dont know whats wrong. im guessing its either the cpu or the mobo from what ive been reading online. i have no idea how to see if its my mobo or cpu that is cause the problem .   im sad cause its my first build and i think i screwed it up . its only been like 3 weeks since ive got it . please help

Here is a video of my pc : http://www.youtube.com/watch?v=2gj4DaQpIKY




i have a :
Intel Core i5-3570K
Gigabyte Intel Z77 LGA 1155
OCZ Fatal1ty 750W Modular Gaming 80Plus