Nvidia GTX 660 acting weird!

[bhaveshzzz]

PC SPECS:

CORSAIR CX 600 PSU
GIGABYTE GTX 660
8GB DDR3 CORSAIR RAM
GIGABYTE GA-B75M-D3H REV 1.0

So guys basically what's happening is my GPU Won't "boot" and I get no signal on screen if I leave the pc off for a long time. Whenever I cold boot the pc I have to wait for around 5 minutes and then restart the pc to get output from the GPU thereafter it works flawlessly until I turn my PC off again...!
I have run CPU burner and GPU Furmark test and I didn't see any artifacts or experience any crashes. No change in FPS in games. All run fine same as before when I didn't have this problem. What can cause this ?

 

[Boozad]

Do you have onboard graphics you can switch to temporarily? If so, remove the graphics card and try to boot using the onboard graphics. Is the machine POSTing when you boot and you just get no video output or is it not POSTing?

 

[bhaveshzzz]

Thanks for replying. The machine boots anyway without the GPU. It just switches to onboard graphics whenever Gtx 660 is not detected on cold boots. Once booted I restart the pc and get output from the GPU. PSU is corsair CX600. Based on a thread here I saw an user who fixed this similar problem of cold boot by replacing the PSU. He too had the corsair CX series PSU. This doesn't happen on all cold boots. It's very random.

 

[bhaveshzzz]

Very Rarely the machine does this too : it starts for a second, stops then turns on.

 

[bhaveshzzz]

Help pls..