Is it sa common fault? If yes how do i fix it? PLEASE!?

Hi there
I have a Ford Focus 1.6 LX 2003 With an RDS 6000 head unit
I recently has a new window motor fitted and when i collected the car i didn't put on the radio,because its onlt 5 mins to my home. Anyway the following morning i tried to put on the unit to play my CD. However the unit would not power up. I assumed that the battery had been off and went and got my book with the code. However it was dead now display at all. So i decided to return it to the garage and get them to check to see what they had done. They checked for trapped cut wires. They checked fuses and said that all was well. There was power to the back of the unit, but it would not turn on.
So then i asked a few people if they knew what was wrong and the response was. Its a thing with Ford the units just stop working. You need to get a new one. I called Ford who said we don't look at the head units just replace them and its around the £300 mark
So can anyone help please?