Please help!

I've purchased a used Ford Mondeo and the AM/FM button does not work, the radio does as it was on when I got it, but after I pressed the other buttons aux and CD I can not get the radio back on.

I removed the button and the soft rubber bits when pressed, do not have an effect. (they do on the other buttons). Also when the other buttons are removed they have a single green light lit behind, but the AM/FM one has two green lights.

Any ideas?

I reckon your button contacts are broken or dirty.
I think they've sold you a tangy yellow fruit.

How do I clean the contacts?
The car was much cheaper than it should have been on ebay, so don't mind spending some money on niggly bits, but will do what I can myself if it's easy enough

You could try a compressed air can like used to clean computers or dismantle the radio face plate to get to the micro contacts but it is fiddly.
I'll talk you through dismantling the radio if you choose to do so.