There is a plastic part which comes loose in the hinge mechanism. This part operates a micro switch which closes when the lid is closed. You need to remove the lid completely. Then shake out the plastic part and snap it back in place. It will be be fairly clear it's in the right place when it operates the switch without falling off. Not a good piece of design. How long the fix lasts, I don't know. Just fixed mine, seems to be OK now. Don't know how it came off in the first place though.
Jez
September 2008