jettalemon

Need a little help here guys. My boss who is in a wheel chair got a system put in his van a few yeas ago, lent his parents his van. Now the display doesn't work he thinks they might have fouled it up by hitting every button. The head unit is a Sony CDX-M8800. Now i have never used a Sony product so i have no idea if it is as easy as hitting a reset button or the whole head unit needs to be replaced. If any one can help me it would be very appreciated.