How much more doesn't work?  Dash lights?  Interior lights?
Have you checked all the fuses?  At least two in the interior fusebox
are related to stereo and clock.  There are more fuses under the
bonnet in fuse and relay box, some of which are very high current and
are in green, brown or grey plastic boxes with transparent lids, one
of these is the main accessory fuse.  Then there is the main fusable
link on the battery - looks like a piece of insulated wire when it's
OK.

Remove the short circuit from the stereo earth or just throw the
stereo away before replacing the fuse.  How long are the screws you
used to to hold the stereo to the brackets?  5mm is max length.

a wire somewhere may be cut or pinched

I have spent hours trying to find the problem, which at first I
thought must of been a blown fuse but all the fuses seem to be in good
working condition.

Check fuse No 24 a 10 amp fuse as this feeds the radio and also the
instrument panel.
Trevor