PC Not Starting At All

My PC has been working great for a while. I recently got a free r9 270x and wanted to install it to learn about crossfire, how to have multiple GPU's, how it works with drivers, etc.

I installed the GPU and realized I needed a 3rd PCI-E plug. My PSU 650W bronze, does not have one. I ordered a 4 pin to 6 pin adapter. I plugged it into one of the sata/periphery spots and used it as my second slot. I think this was a mistake but I'm not entirely sure this caused my problem.

Upon trying to turn on my computer again, I am getting no response. I've checked every plug, taken out all unnecessary additions (including the r9 270x) and the extra plug.

I was concerned maybe i burned out my PSU or MOBO, but there was no weird smells, no sparks, no nothing to give me any sign that something malfunctioned.

I did notice that my MOBO is SUPER HOT. Like The computer has not been "on" for hours and a part near the PCI-E 2 slot is too hot to touch. Again, the PC's been off for hours.

TOmorrow I;m going to get a safety pin to see if the PSU works, but I don;t think it's burnt out, again, no smell, no spark, no nothing.

Anyone got any ideas where to start? I've recheked all the plugs, cables, and will do so again tomorrow.

One green ligh is on on the MOBO, not blinking or anything. I believe that that light is usually on, but i scowered the manual for a long time and for some reason this one light is not documented that I can see.