I've a 13yr old freezer that's made in germany.It was workin fine until
yesterday when the compressor did something funny. Usually, the
compressor will switch on , due to the thermostat i think, then off
when it reaches the temp required. but now when the compressor switch
on, it immediately switches off. There's a tempwarning light that's now
constantly turned on. It will occur for quite some time. I also realise
that the compressor itself is very hot, you could only put your hand on
it for a couple of seconds.. Can anyone give me some pointers on how to
repair it

Sounds like the compressor has a locked-rotor, meaning something broke
and has stopped it from turning. Rather than start a fire from
powering a motor with a locked-rotor (draws many times normal running
current), I'd unplug it, and shop for a replacement for the freezer.
Your fire-marshal will thank you.

HTH,
J