I had exactly the same problem. I replaced the door locking mechanism (around £30) but that didn't fix it. It turned out the circuit board had blown near one of the connectors (they're all at the top front of the machine under a cover, if you take the top off-look for scorch marks!). New boards are up to £160, so we repaired it ourselves with a bit of soldering...and it actually worked! Result.
michael byrne, August 2007