Hello Fran,
I suspect that the nylon gear under the raceway in the bottom of the machine has broken up, very common on the 400 series especially considering it age, take the bottom off and have a look, then take the top off the machine and have a look at the nylon gear because that may be broken, it can be fixed without an expensive shop repair, I have all the instructions, email me below with your findings.
ken
drivewithken@blueyonder.co.uk, February 2009