try these things to check where the prolem lies
remove battery try to start from power unit.
any joy. no ?
try this stat once more but hold the swithch down for a minute let go,wait a minute then try again. Y ou trying to establish whether it is a switch problem or some other component.
NOW repeat all above with battery in and mains disconnected.
Still no luck then its a repair shop job- who may turn the job down depending on age of machine and parts availability.
Workshop costs run at 60 quid an hour these days - is the machine worth a couple of hours to find it is not repairable?