I started having this problem the day after I'd sold the car, when the buyer came to pick it up. Needless to say I still have the it.

Basically I took out the aftermarket stereo, which had never caused any problems, and reinstalled the original one, which began working as it should straight away.

5 minutes down the road, on the way to the bank with the buyer, the engine cut out. I restarted, and it cut again. This happened a few more times, then it wouldn't start at all - as if the battery was completely flat. Then 30 minutes later it came back to life and started, but then kept cutting out.

The AA diagnosed it as a knackered battery and we changed this, and afterwards it seemed to work fine, however the problem has now recurred and additionally the alarm started randomly going off too.

Any ideas what it could be? Is the stereo changing business a red herring?