Oh so many things, ensure all cables are connected correctly and nothing has got knocked in any way.
have you tried plugging into another socket that you know works ?
Another thing you can do is reset the cmos memory via the jumper. I wouldn't have thought this would fix the problem, but it's a harmless thing to try.
So are we to assume that a shop made it for you?
You can only hope.
So you took it into a shop and they charged £15 to test it, and want £40 to fit a new one?
It's not hard to fit a new one, getting the wires tidy can be a pain.
Just 4 screws and lots of plugs!