How can i fix my Ford Focus Radio?

My 52 Ford Focus radio has decided to break! After about 20 mins of my journey on my way to work, the radio looses the signal for all the stations. When i go home, again the radio is back on until it decides to loose the signal again. This has happened for the last week or so! I have removed the aerial from the roof and made sure it is put back properly but apart from that am at a loss.

Tina
January 2009