Friend bought in a computer complaining it wouldn't start up. I decided to use my own monitor to test it.My own personal WTF resulted in me unplugging the cord from the monitor and plugging that into the computer. So the DVI cable was running from my (still powered on) computer to his computer.
Messed around trying to figure out why it wasn't showing anything on the screen then while I was marvelling at my own WTF, I noticed something odd.
The case fans(which had pretty blue LED's, and were connected to the PSU) and CPU fan were still turning. Not so odd you might think, until I saw that I had also unplugged the power cable. The ghost fans stopped when I unplugged the video cable, and started again when I plugged it in.