crossfader serato dj pro not working

I have djm 900 nexus 

and serato dj pro on my Imac...

all was working and one day the crossfaders all  do not work in the serato

so I can not mix videos ... 

I have looked for help I have all updated  I have no idea what to do to  I have tried to re map.. im no pro but it was not rsponding and yes the midi light button I have on on the mixer....