I went to install a second graphics card (NVIDIA 260 GTX) and when I hit the power button, it flashed on for a second and powered off immediately. Now I can get it to even turn on.

I didn't smell or see any smoke.

I removed the second card and it still won't turn on.

I tried placing the first card into every available slot and no go.

I put my old card (NVIDIA 9600 GT) in every available slot and no go.

I unplugged and reattached all cables...still nothing.

I cycled my PSU and still nothing.

When I turn on the PSU, it looks like some LEDs (a power and reset switch near the bottom of the board) on the mobo are lit, the sound card is lit (the mobo comes with its own), but it just won't turn on.

I think I may have connected the new card to the wrong plugs on the back of my PSU. My cards take two 6-pin PCI-E cables. I had two open 6-pin plugs on my PSU. But after closer inspection, I saw that those two plugs were actually labelled "4-pin peripheral and floppy connections" or something like that. Two of the PCI-E plugs were being used for the first card and two other 6-pin plugs were being used for my optical and hard drives (they were labeled E-SATA I think). The sole 8-pin plug on the back of the PSU was hooked up to my mobo, the 24-pin cable was connected to my mobo, and I still had two 8-pin cables coming straight from my PSU, but had no 8 to 6-pin converters, so I didn’t use them. They weren't connected to anything. It leads me to believe that there was a voltage difference and I fried something when I used those "floppy" 6-pin plugs on the PSU to connect to my video card.

My PSU is a Thermaltake 850W Toughpower and my mobo is an ASUS Striker II Formula.

Any ideas, help, suggestions?