My iMac is not encoding DVDs,I tried to burn music or softwares and does it with no prob,but burn movies or encode doesn't do it,I ran disc utility test and everything is fine,How can I fix this,my first yr of warranty expired from apple,Is there anyway to run a test to see if the lens are dirty or to try to buy a disc cleaner,I need help on this please,I don't think this is broken since my imac is 16 months old.