Everything's in okay. I was very, very careful not to displace anything. - Also, the computer doesn't seem to be on. None of the fans spin or anything, but the green light comes on (hopefully) signifying it's receiving power.
Don't tell me the PSU is DOA.
Make that a last resort!
The PSU is dead, isn't it? I'm reading that the green light doesn't necessarily mean the PSU works.
Yup... It's the PSU
I plugged in my old PSU into the MB (just the MB) - and the fans turned on and everything.