ALRIGHT! Had a couple of 12-14 hour shifts at work. Came home dead tired. Couldn't be arsed with the PC - until today.
Bought the buzzer for the mobo, didn't work (not sure if it's a good match, just some random buzzer - it doesn't work).
Didn't try and heat it up because of the lack of time...
Didn't check if everything was connected properly because of the lack of time...
What I did manage is to drop the case side and scratch the monitor. YAY...

So I'm sitting next to it, browsing the interwebs on the phone and it just pops into my mind "power it up, it will start!". I power it up and nothing happens, so I just go back to the phone. 10 minutes later I hear the CD reader go: "chhh, chhh, chhh", I see the 3 LEDs on the keyboard flash and it starts. First it went into BIOS saying something along the lines "POST error, blah blah blah", restarts and boots normally???!!!?!?!11!
Just wanted to update you and say thank you one more time, but apparently this PC has a mind of it's own. I did manage to find a new PC which I will probably end up buying but it's a less of a rush now.
Lesson learned, clean your PC in time:
Pre-cleaning CPU temperature - Core#1 literally displaying "/", occasionally dropping to 95°C, and under max. it says 95°C.
Core#2 95°C
Post-cleaning - Core#1 46°C; Core#2 46°C


