In reply to jon:
Leave it off for a day then try it. Some have a resettable temperature switch so have a look at the pipework and press anything obvious (with the power off) then try it, if it has a switch that tripped it might be nothing and run for years more or it may trip again.
Repair wise, a new compressor is about £80 plus vat, maybe £30 or £40 in gas. There may be leaks in the pipework that need repairing. Then the time taken to fix it, for industrial refrigeration the going rate is £50 to £80 per hour (plus vat), for domestic I don't have a clue.
If it won't reset bin it and buy a new one. If you can't fit the old one in your car to go to the tip pay whoever sells you the new one to remove the old one. Once upon a time you could leave one on the street and our traveling section of society would take it but scrap yards won't touch them now. Too much insulation, not enough metal and the gas regulations to deal with.