How I can fix my Dirt Devil 1400W Cylinder Vacuum Cleaner?

This machine has not had much use over the past three years. However someone has used it and extended the electric lead beyond the red marker - this might not be the problem, but there is no power now. I have checked fuses blockages etc.. I want to get inside the casing to check the lead and the two switch mechanisms - on, off and extendable lead - but can't seem to get beyond the three screws holding it - are there any other screws I am missing. Or can you suggest other remedial checks. It's not an expensive machine but I am loath to give up on it. Help would greatly lift my spirits!