Mine is completely dead and it was brand new. I bought a new iMac in October 2015 along with the superdrive. Plugged it in and wouldn't accept any disc, just kept spitting it back out. Tried all the solutions other people have suggested and none of has worked! Beyond p*ssed because I could have saved myself £65 if I knew it wasn't do anything.
My iMac is on Yosemite, haven't downgraded or upgraded, nor do I plan to because I heard El Capitan is crap. I've located my superdrive in the disk utility but it comes up grey. You can click on it but it just tells you how to erase a rewritable CD/DVD so I can write on it again but I don't have any CDs/DVDs on me that I can do this on since I'm away from home. Only options I have at the top of the disk utility window are "info" and "burn". Other options have been greyed out.