The friend explained that their PC wouldn’t start up.

“Where do you keep it?”, I asked.

‘On the floor’, was the reply.

“You need to give it a clean, it’s full of dust.”, was my psychic reply.

This friend keeps multiple pets, dogs/cats/birds/lizards.  The poor PC was sucking all the assorted animal dust/fur off the floor, for the last two years, and finally gave up.

So they cleaned the PC, and it still wouldn’t start.  They passed it over to me to look at.  When I opened the PC case, the video card cooling fan looked like this:

dirty card

(yes, that’s dust which has defied gravity and managed to bind upside-down to the heat-sink)

So I pulled the PC apart and cleaned it.  Slowly re-assembled it, and it all worked.
(and the PC spent the next 2 hours applying Microsoft Windows updates, which it hadn’t done since May last year.)

When I gave the PC back, I noticed I’d missed a spot. Sad smile