Try both a CD and a DVD, could just be one laser busted.
That said I went with out a optical for a long time. Any USB external is OS X compatible. Just some dont do boots. Generally those slim ones that power off the USB dont boot. The full size externals like a LG do and are faster then even the built in one you had. I picked up a lightscribe LG last year because i wanted to make some nice photo DVDs for a friend. Still hardly use it but when I re ripped all my CDs, man was worth it with the speed it has.