I'm having an issue with either my graphics card, my power supply, or one of the 6-pin PCI-e power cables.
My computer won't power on when my nVidia Geforce GTX260 is plugged in (with 2 6-pin power cables). If I take out the GPU and plug the display into the on board video, my computer will turn on and windows will boot. If I install the GPU and don't connect the 6-pin power cables, my computer will turn on and windows will boot, but I will have no display (sounds reasonable, as the video card isn't receiving power). The odd thing is that my computer will turn on and boot to windows (no display) when only one 6-pin power cable is connected to the GPU. When I power down the system and connect the second 6-pin power cable, the computer won't power on. If I completely remove the video card, I have to unplug the 24-pin MB power cable and plug it back in before my computer will power back on.
Does this sound like an issue with the 6-pin PCI-e cable, the power supply, or the video card? The cable that doesn't seem to work properly is a 4-pin Molex to 6-pin PCI-e power cable adapter. I haven't had any issues like this so far while owning the system (over a year) and it was even working perfectly earlier today. My power supply is a 550w PSU.
Your PSU is probably too weak to run that card. According to this: http://www.tomshardware.com/reviews/geforce-radeon-powe...
you need slightly over 15A to run the card at load. Half your 12V power is going to the card.
Nvidia states you need 36A to run a GTX260, which is an overstatement, but you'll be hard pressed to power half that.
Now, it should power on, at least, with those currents, but I guess I can't blame it if it doesn't. It does explain your situation, though - when you give it access to only one 12V rail, the system boots because it still can draw energy from the other rail. When you give it both rails, it won't boot because there isn't enough current to go round. Remember, those rails power the rest of the system as well.
What brand is your PSU? If it's not good quality one, it may not even be living up to it's sticker currents.
All in all, I'd get a new PSU. I can't really say why it won't at least boot, but you don't have enough power to run the card at load anyway.
Edit: I missed the part where the system has been working for a year. But as your PSU ages, it loses some of it's ability to push current, which can help explain this.
Thanks for the responses guys. I'm going to try replacing the 6-pin adapter tomorrow and if that doesn't fix it I will begin searching for a replacement PSU.
I appreciate the help
You have been deceived by Thermaltake.
Here's what Hardware Secrets found during their testing of the Thermaltake Purepower 500 W power supply:
To start off, we can’t believe that a company like Thermaltake is still labeling some of their power supplies with a fake wattage. This should be illegal. Officially this unit is a 405 W power supply, however we couldn’t pull 400 W from it for more than a few seconds, meaning that this “official” wattage is also unrealistic, as it was probably measured at 25º C (we test power supplies with a room temperature of at least 45º C and the power supply ability to deliver power drops with temperature).
Being able to get only 375 W from a 500 W power supply is not the worst part: starting at 310 W +12 V outputs were presenting voltages lower than the minimum allowed, offering real risk to your components.
Since this unit achieved its maximum efficiency at 145 W, we can easily say that this unit is in fact a power supply between 240 W and 360 W.