Powers off after half a second

[Shiggity]

So I just built a new computer and everything worked for a day or so, but I tried hotswapping the DVI cable that was connected to a PNY card to the other port (so I'd have room for the antenna off the wireless card, but that's neither here nor there).

Got no video, so I shut down the computer and for some reason it wouldn't start! When I pushed the power button in front (XION case) the lights and fans started for about half a second and then it went dead. I could duplicate this by cycling the PSU switch and repeating. If I left the switch on but just tried pushing the button again, it did nothing at all.

I unplugged the DVI cable, cycled the switch, and the computer started (but now no video).

I got it to work again after I switched to another DVI cable. What is wrong here?

Please note that (1) This cable has worked for years on another computer/monitor combination and (2) even if using the new cable will work from now on, I think it's important to know why having a video cable connected would prevent a computer from starting.

Stats:
ASUS P5E3 Premium MB
PNY nVIDIA 8800GT video card
2 DDR3 ram
PATA HD (Western Digital) and DVD-ROM on same ribbon (cable select)
Thermaltake Toughpower 1200W PSU
Intel Core 2 Quad Pro (not the thousand dollar one)
PNY card connected to 12V PSU outlet
The rest connected into peripheral PSU outlets

That's it I think. Thanks for any help.

[Shiggity]

Update:

The second time I tried powering up with the new cable it happened again. I tried using a new monitor, new monitor power cord and new wall outlet, and still the same.

However, I notice a number of successes when the monitor is left off. I don't recall ever failing while the monitor was off. Also, I'm able to succeed with the monitor on, either arbitrarily or because each time it succeeded with the monitor on I waited longer between the time I flipped the PSU switch and hit the power button.

Still in need of help, just giving more information.

[Chaky]

That, my friend, is usual behavior of short circuit protection. Your PSU detects a short circuit, immediately shuts down and refuses to start again, until it is reset. And reseting is done by switching PSU switch off and on.

You should test the machine with different monitor, because it is a prime suspect. I wouldn't recommend trying that monitor on different machine to see if the problem is reproduced there, because it could fry that other machine.

While you are still testing the newly built machine, I would advice you to disable quick POST in BIOS. It will make BIOS run extensive tests on boot-up, significantly prolonging boot time. After couple of successful boot-ups, reenable it, to speed things up.

Word of advice: Don't use DVD-ROM on cable-select and on a same cable as HD. Set it on SLAVE and on a secondary IDE port. Set HD on master (or single drive, if available).

Also, in BIOS, disable auto-detection for unused drive ports. It will boost your booting time.

[Shiggity]

Thanks for the reply!

I'm glad it's a protection mechanism and not an explicit failure. Unfortunately I could duplicate it even with a different monitor, DVI and power cords, and wall outlet.

Also, I have only one IDE port on the motherboard, which is why I used the same ribbon. Thanks for your other suggestions also.

That, my friend, is usual behavior of short circuit protection. Your PSU detects a short circuit, immediately shuts down and refuses to start again, until it is reset. And reseting is done by switching PSU switch off and on.

You should test the machine with different monitor, because it is a prime suspect. I wouldn't recommend trying that monitor on different machine to see if the problem is reproduced there, because it could fry that other machine.

While you are still testing the newly built machine, I would advice you to disable quick POST in BIOS. It will make BIOS run extensive tests on boot-up, significantly prolonging boot time. After couple of successful boot-ups, reenable it, to speed things up.

Word of advice: Don't use DVD-ROM on cable-select and on a same cable as HD. Set it on SLAVE and on a secondary IDE port. Set HD on master (or single drive, if available).

Also, in BIOS, disable auto-detection for unused drive ports. It will boost your booting time.

[Chaky]

Since it is newly assembled machine, almost anything can cause short circuit.
If you say that you can duplicate with different monitor, then it leaves 2 things directly related to this problem. Graphic card and PSU itself.

For the graphic card, you can try reproducing the problem with no VGA (if there is no on-board VGA). This is bit far-fetched, since you won't be able to get past the POST process, but there shouldn't be any immediate shutdowns. Only beeps, if you have the beeper installed.

Oh, yes.. DO get a beeper. It is VERY useful tool for troubleshooting. You might be getting beep-codes right now telling you exactly what is failing. All you need is a simple PC speaker. You can salvage one from any old PC.

For the PSU. (Consider this as a last resort)
With 1200 Watts, term "lack of power" can be only used as a punch line. But, it can be faulty and the protection shut-downs could be bogus. My best advice is to try another PSU if possible. I know that replacing PSU is a pain in the neck, but you can't be sure if it is causing the problems or not, unless you eliminate it.

Before you replace the PSU..

As I said, since you are dealing with a possible short circuit, virtually any piece installed can be causing it. From CPU to USB jacks. You will need to double-check all of the wires. Especially fire-wire and USB ports. Also, try reducing the functional hardware to a minimum. 1 memory stick, VGA and HD (and nothing except the switch connected to the motherboard) and see if you can reproduce the problem then.

Good luck with hunting.