My macbook pro (the older kind) won't read DVDs anymore. When I put one in, it either spits it right out, or lets it sit and won't recognize it. My application DVD Player can't recognize the discs. I can't even run one of those laser-lens-cleaning DVDs. This is a big problem, since I'd like to upgrade my OS soon to work out some of the problems that have been popping up lately. But I can't do that as long as my computer rejects DVDs. (It can read audio CDs just fine.) What can I do about this?