I think I fried my motherboard (and I have no clue how)

[Phocephus]

Right, so heres how it started.
I noticed my GPU temperature at idle was at 83C and obviously I felt like that was too hot. I wanted to investigate.
I assumed it was just dusty, so I opened the case, disconnected the PC (after shutting it down normally).
I saw how the GPU actually wasn't really dusty at all. But, I noticed the opposite side of the PC (as it is standing up, to my right from the chair) was open. Like, the panel wasn't on.
I concluded that the airflow wasn't circulating due to it being an open case...

I slid that panel on, and then flicked the power supply back on. I pressed the power button..

..nothing.
This was strange, the power button suddenly just STOPS working. Anyway, I wanted to try to jumpstart the motherboard doing the screwdriver-to-the-pins trick. Of course, I did this after testing the power supply (you never know!).
The GPU was actually hovering over the front panel pins, so I took it out and disconnected it from the PCI-E port and powersupply.
I set the screwdriver to the two pins, and nothing happens.

Is my motherboard.. just.. gone?

 

[Nine Layer Nige]

Please provide motherboard make, model and CPU make, model.
Any beeps?
Can you start up without the GPU installed ?

 

[Phocephus]

Please provide motherboard make, model and CPU make, model.
Any beeps?
Can you start up without the GPU installed ?

Turns out the 24-pin was just half a centimeter out. I didn't notice because the room was dark. But the case power switch is actually broken. Thanks for the concern, though.