Switch it off at the mains.

Get a screwdriver and unbolt any screws you find on the back and sides
of the main case.

Take of the main case: it usually gives up to a hefty shove, pull and
slide motion.

Look inside, near the front and look for a rectangular metal box, or
two sheets of metal enclosing a cylindrical thing, like an undersized
CD, but up to an inch thick.

It will be attached with more screws and a few pluggy things (flat
with lots of holes, like a miniature bar of chocolate) usually its
got a fat wire looking like unstretchy elastic attached.

Haul that out and destroy. That was the hard drive. Your machine is
now brain dead. Check if it has a donor card and dispose of its
innards to the charity of your choice. They will make good use of it.

Ours go to the boffins at the local university, who patch them up,
insert new hard drives and so on and ship them out to Africa, India
and other places who need them. They enjoy the challenge. It keeps
them off the streets and the computers get a new home. Win:win.

Does that help?

Nel
(GQ) who has disembowelled more of these than is strictly healthy!