Have had the same problem, prewash light flashing right hand side of machine. The shop I purchased machine from have spoken to their Engineer and it's a case of re-setting the machine. Have told me how to do it and the machine's working again - fingers crossed!
Turn power button off (not at wall)
Select 90 degree wash
Press Start and Cancel button down at same time for 3 seconds and turn power button on whilst still holding buttons down - Start light will flash.
Leave power on.
Select any Spin position.
Press Start and Cancel button at same time again for 3 seconds - other buttons may start to flash - if they do, press Start and Cancel button together again for 3 seconds.
Machine should be re-set ready for use.
Good luck!
Dave, March 2008