Is my PCIe x16 Slot dead??

Hey There's
Alright, I think my mobo PCIe slot is dead, Ill give you the run down, please feel free to add any idea's or things I missed

I have a Dell that was transferred to a Larger ATX case to accommodate a Evga Nvidia 9800GTX+. It originally had a ATI X1300. Also upgraded to a 500W PSU for the 9800GTX+. I wouldnt call myself a computer whiz, but I have worked with electronics long enough to know how to carefully remove and install parts. I Installed the New 9800GTX+, installed updated drivers, and it works great for 2 days, then I go to turn it on one day, and I only get a black screen. I can hear the hard drive working at startup and I can hear the Windows Vista Startup chime, but only see a black screen. I open her up to check connections, seems to be seated correctly and tight.

1st thing I think is that somehow the mobo Integrated graphics card got switched on and it disabled the 9800GTX+. Swapped monitor cable over to the Integrated port, and I get the dell logo on the monitor, I go into BIOS and the video setup is set to "auto" (dell only has 2 options: "Auto" and "Onboard/Card", oddly dells explanation of the 2 settings makes them sound like they both are the same). Switched settings and rebooted several times, no change.

I went back into BIOS to look at the what the computer says is connected to the PCI slots, and it shows nothing, all slots empty. Thought I would reboot to recheck these results, and this time it detects a VGA (9800GTX+), I hook the video cable to the 9800GTX+ back up, and there is no change, still only a black screen, I go back to the integrated graphics, go back into BIOS, and now it says that again the PCIe slot is empty. I thought next I would update the BIOS, which I did, and retested everything using the same method from above, still no change, just a black screen.

next Im thinking the 6 pin power supply wires may be to blame, however the 9800GTX+'s fan is on and working normally, but I go ahead and take the molex adapter that came with the 9800GTX+ and give that a try, Still no change in the results, just a black screen.

Lastly I take the old ATI x1300 card and plug this into the PCIe slot and still thats all I get is a black screen. Checked BIOS and its says still that the PCIe slot is empty.

I have examined the PCIe slot and it looks fine. No broken connections/solder, no corrosion, no black or pitted areas, same with both graphics cards, all clean. When the card was working, system temps were only at 40c max (both CPU and GPU) so I dont think heat could be an issue. This is where I am now.   Im thinking new motherboard, thoughts? thanks!