Had this problem on mine, I disconnected both terminals from the battery, and touched the earth and positive cables together for about a minute I then left both cables disconnected from the battery for half an hour and then reconnected them to the battery,
A very experienced auto electrician told me to do it, he said that by touching the two leads together it discharges capacitors in the radio unit which resets and clears issues, he says there is a TSB regarding issues with for Ford Focus radio heads and the method I have explained is method to correct it.
it worked for me