I left it for 10 minutes, maybe longer, and it just stays black screened with the buzz sound. The longer I leave it off, the longer it lasts without doing this
This sounds like a overheating issue. The longer you leave it off, the more it cools down making it run longer until it heats up again and gets hanged. Check your CPU and GPU temperature using hwmonitor. https://www.cpuid.com/softwares/hwmonitor.html
I'm no computer whizz, so I don't quite understand at which point I should be worried. On another note: I had the computer plugged into a multi socket, would that maybe have caused it?
You should be looking at the temps. The screenshots are showing normal temperatures. I wouldn't rule out multi socket but I personally use it too. I noticed that the voltage readings are missing too.
hmm, the strangest part is, it crashes when I'm not actually playing any games. Happened when I was just listening to spotify etc
GPU problem, make sure driver is updated (If updated then reinstall). Then download GPU stress software and run it, if it does the same thing even faster then your GPU is fucked.