How can I fix my Hoover Vision HD Washing Machine?

When I select a program and press the start/pause button it normally clunks (door lock) and starts filling immediately....recently it has started to every now and then not do this.... but if I twiddle the selector button it has eventually clunked and worked....It will not do this at all now, it is still lighting up etc so not the fuse (as the FAQ section of instructions booklet suggests)....I have turned off at the plug to give it a chance to reset etc but not having any luck......Help