Computer turns on for around 1 sec but fails to start

Hey guys

I'm having some trouble with a computer I've built over the last year.

I went to turn it on about a week ago after it had been off all night and it wouldn't start up. The fans all come on for about a second but then it just never quite manages to come on. I had the same problem in September but in the midst of trying to diagnose what part was the problem, it stopped happening and started workinbg. Ignorance is bliss and so I carried on with the computer working without any issues until a week ago.

I thought the problem might be the PSU, I had a Corsair TX650W (I was tempted to believe this might be the problem as I had some problems with this PSU being faulty two years ago and had to have it replaced by Corsair) however, over the weekend I bought a new PSU, a Corsair GS700. It came first thing this morning and I plugged it into the motherboard and lo and behold, same problem is occurring.

After the PSU I feel like the problem might be the Motherboard or CPU, hence where I have posted this. I don't know how to find out what the problem is so any help you can provide would be much appreciated.

So I am totally lost. I'm about to go and take off the CPU Cooler to make sure it isn't a heat sync problem but I just don't know what to do beyond that and am totally stressed out as I have two weeks until I've got some major deadlines and my work is stuck in limbo on my computer.

Computer Specs are

ASUS SABERTOOTH Z77 Motherboard
Intel I7-3770K, 3.50GHZ, 8MB Cache, LGA1155, 77W
GEFORCE GTX 680 2048MB
CORSAIR TX650W/CORSAIR GS700
CORSAIR Force Series SSD (Sata 3)
Kingston HyperX DDR3 3x2gb

So yeah. Thanks for reading guys, hope you can help please do get in touch