Power issues

Hello Everyone,

I built a rig with a friend 2 weeks ago, installed everything and it was running fine first few days (Nothing is Overclocked and i don't plan on it ) however for the last few days it works fine, but when i power down the next day it wont turn on :S . I push the power button and i see the fans light up for half a second but they don't spin, and then nothing. The green light is working on the Mobo and normally i sit there unplugging cables from PSU and GPU and mains etc and eventually it starts and works fine all day, then a day or 2 later it happens again. I know this is long-winded so thanks for reading  

PC build of the top of my head is:

OS - Windows 7 ULTIMATE 64BIT
CPU - intel quad core 2.4GHZ
Mobo - ASUS P5G41T-M LX
GPU - Nvidea 9600 GSO 768MB
RAM - Kingston HyperX 8gb
PSU - Modular PowerCool 750W

Any information is greatly appreciated, im hoping its not the PSU as it works fine all day >.<