So because Apple sucks I had to spread my three photos across three posts instead of attaching them to only one as all images I take are just named 'image' and I can't rename them without third party apps.
Anyway I think I dun goofed. I did buy a new GPU and built it in, only it now occurred to me that what I removed might also contain the processor instead of only the GPU which would explain why now my PC doesn't show anything on screen when I boot it up.
On the first two photos (my last two posts) you can see whatever it is I removed, at least my old GPU though maybe it contains the processor as well, in the one in this post here you can see the new GPU I built in. If my assumption is correct and the processor and my old GPU are indeed on the same piece of metal I guess I'm up a creek as there's no way both fit onto my main board.
Soooooo... wat do?
Edit: Oooooooor maybe th HDMI cable just wasn't plugged right in or this is one of those stupid graphic cards that don't work for TVs. Whaddaya know, I put the computer in my room again and connected it to my regular display. Hmmmmmm, things seem to be working for now, call me cautiously optimistic but I think I might just have solved all my problems...
Edit #2: Aaaaaaaaaand two minutes later the PC rebooted, because things can never just be easy.

I was even editing another screenshot of HWMonitor as it happened, but now you'll just have to be content with the old photo I took and reuploaded in this post. While all other temperatures are now fine the third TMPNUM thingy in the first entry (Gigabyte Technologies something, my motherboard I believe) is way above the rest, 40 degrees Celsius versus 30.
Another Edit: A friend of mine has brought the possibility to my attention that the power supply unit might be at fault as 40 degrees is not even close to overheating. I guess that's as good an explanation as any.