This is an utterly non-technical reply, but hope it helps. Could be lots of things but we have one of these fridges and when we had a similar problem found that turning it off for a day (or longer) fixed it. Apparently there was a build-up of ice somewhere inside that was stopping whatever it is that makes it cold from working properly and making it overheat. Quite a bit of water came out the bottom after it was turned off. I know that this isn't an attractive solution but it's cheaper than buying a new fridge. I also know that they are supposed to self-defrost, but hey, it worked.
The thermostat could also have gone, have to get the technician out for that one.
Good luck.
Clare, September 2006