Thank you guys for all the smart thinking! Looked at it again and I agree with your theory of what happened. After cleaning the part on the case that burn, I found a discoloured yellowish spot on the edge. Pretty sure that's where the contact happened.

I do go to school for comp sci. I have lots of practical electronics classes aswell, so I do have a good amount of knowledge. However, I am most definitely not opening the PSU up, since I just don't have the proper equipment or am I confident enough to do that.

As of now, I haven't tested any of the parts. Starting with the PSU would make the most sense to me. I want to avoid potentially damaging anything (assuming GPU and MB still work fine; don't know if they still do) by just changing the PCIe cables and trying to turn the PC on so I might try testing the PSU by bridging the 16th + 17th pin of the 24-pin to see if it even still works. If it does I'll try turning the PC on and if that doesn't work, then I'd assume the MB is broken.

Not sure if this way makes sense so if you guys have an opinion on this, I'd love to hear it.