Kate,
if you're in the UK then there will be a fuse in the plug - but no matter - if the machine works in reverse then you can ignore the fuse as a cause.
Your problem is that the machine runs in reverse but not forward.
If the motor hums when you select forward then something is jamming the mechanism - but I suspect that the small micro-switch that detects paper entry and gets the machine to run is either stuck or not working.
I have no other answer for you - sorry.
Continuing Good Luck..., April 2016