Djm 900nx2

Hi,we buy for the club a mixer 900nx2 new,and I got this problem,after a few hours the lights from volume get block in all the channels.thats one problem,other problem sometimes sound stop and I have to put off the mixer and put on again for the sound come back,and another problem is..after a few hours the sound change to a really bad quality.all this problems doesn't happend together,the problem I always have every nights is about quality sound, base go really down,and highs really high and master volumen come down changing the volumen.whats goin on?