Switching fan on nVidia card

I just switched my nVidia 8800GT VGA cards standard fan for a Vortexx Neo fan, and once I'd put the card back into the machine, plugged it in & the Vortexx, the machine boots, hangs and then shuts down. When it boots, all the lights come on, fans start up, everything as normal for 5 seconds, then it shuts down and after another 5 seconds it tries to boot again. Nothing else has been altered whilst I changed the fan, the machine itself is still pretty 'new', having been built just a year ago now with new parts.
It comprises an ASUS motherboard & quad-core Intel 2gHZ CPU.

I've tried switching back to the standard fan, but the computer still will not boot, and I'm worried I've somehow fried the VGA card (I have carefully applied the heatsync to it). Nothing has gone bang, or smells... so I'm quite confused.

Any advice?

CPU is usually the last thing to go. PSU is most common, followed by Motherboard/RAM.

I would take it to a local PC shop if there is one near by they could point u in the right direction if you don't have any extra hardware laying around to swap in and out.

Most of the time they will test the PSU for free if u ask them. I know i always did since it only takes about 5 seconds if they have a tester.

Having them tell you whats wrong will cost money but it will save u the headache and time of buying new parts and just kinda spinning the wheel on finding out what the problem is.

Also never take a computer to Geek Squad.

I've gotten the PSU checked out, its fine according to the PC shop I took it to. My personal engineer (well the guy who built the machine) thinks it could be a cracked GPU on the 8800GT. The system won't boot wih the VGA in and it won't boot without it. There is not an onboard VGA card for me to check, so is there any way I can tell if the VGA GPU is faulty (physical signs)?

Other suggestions I have had thrown my way are a surge from the PSU damaging the Mobo or that the HDD is at fault.

I'm not getting any beeps or noises at all whilst the speakers are plugged in and on.