Anyone know how to fix Kenwood Car stereos?

My Kenwood KDC-BT6544U car radio has decided to stop playing anything from any of the sources ie. the CD, USB socket and ipod jack. Still plays the radio no problem but it doesn't recognise any source at all.

Hasn't had any knocks or adjustments, just stopped around mid-December when the weather started getting really cold. Could this have anything to do with it???

Typically it is 14 months old and came with a 12 month warranty!