Dvd recorder randomly restarts

We have a Panasonic DMR-XW300 dvd recorder (with 250gb hd and two digital receivers). I love using it but it has a problem. While watching and/or recording, it will restart for no apparent reason. It is intermittant and may not happen for weeks and then do it several times in a few hours. Usually it restarts and goes back to viewing and if recording it creates two files with a time-gap between them. Sometimes it just shuts down and we have to manually turn it on again. Sometimes it loses it's memory and we have to set up all recording again. If we don't realise it's happened, we find our shows haven't recorded which is very annoying. It's in the shop and they seem to want to see it happen so they can get an idea on what's wrong. This may take a long time and chances are when it finally happens they'll be out of the room.
Help! - any clues will be greatly appreciated!