Power off. Check the interlock - it has an internal switch which supplies power to the rest of machine. Non repairable, if faulty - replace. Possibly a duff connection on one of the board connectors. power off, remove covers, disconnect circuit board connectors and clean with toothbrush. May help to tighten them with a pair of pliers. Clean off any corrosion or crud, refit and test.
Check out this site for info: www.2ndwave.co.uk/manual.html
Check out this site for spares : www.4directelectricals.co.uk
dan, February 2008