Try to give a bit more information when placing a question - the more info , the more chance of identifying the fault.
Power off, drain machine by running the outlet pipe into a bucket at floor level or run the outlet pipe out of the back door if it'll reach. Drag machine out onto the floor, remove back and top cover. Some interlocks prevent the door from opening if the drum is moving. The mechanism that detects this is called a pecker unit and it is located around the motor pulley. It connects to the interlock via a cable assembly. If the pecker unit is broken in the "on" position it may be preventing the interlock opening. Visually check and try to activate the mechanism by hand.
Other interlocks have a secondary locking system which ties in with the pressure switch - the mechanism which detects if there is water present in the drum. If this system is faulty - caused by blockages in the filter, pressure vessel or the thin rubber pipe running to the pressure switch the machine "thinks" its still full of water and wont allow the door to be opened. Take off the top cover, examine the interlock from behind and detach any rubber pipes or cables to try to open it from inside. If all else fails, the interlock itself may be faulty and will have to be broken open. A replacement interlock unit and/or catch will of course be required. Typical interlock replacement: Power off, remove mains plug. Remove the plastic band that holds the rubber door seal to the front cabinet. Un-hook the rubber gasket from cabinet lip on the door lock side. Put your hand in and hold the door lock whilst removing the 2 screws you can see from the front. There might be a pressure pipe attached to the lock, if so, just pull it off. Make a note of the position of the connectors and disconnect wiring. Refitting is, as they say, a reversal of the above process.
Check all wires and connectors generally for internal breakages or wear of the insulation allowing the wire to short out - caused by movement of the wiring loom attached to the drum. Over a long period of time the wire strands inside the insulator break through metal fatigue. Although the outside of the wire appears ok the internal is open circuit. Pull on each individual wire - if theyre ok internally, they shouldnt stretch.
Repair and service your own washing machine. Go to www.2ndwave.co.uk/manual.html
dannyboy, March 2009