I've seen CD-ROM and DVD-ROM drives go bad after a while. Even seen one where it was bad straight out of the box (no wonder it was on sale for a ridiculously low price). Easiest solution is to just simply install a replacement and see if the problem goes away.

Ah yes -- one other thing -- for CD-R and DVD-R avoid Ritek brand -- I know a lot of people who have had reliabilty problems with the media (disk is OK for a month or two, then start having errors -- after about 6 months the disc is unreadable).

Speaking of bad media... I once saw a batch of "no-name" CD-Rs where the foil layer was translucent. The disc would often read OK -- until you wrote something with marker on the label side. If you had written on a self-adhesive paper label.it was slightly better (reliability was directly connected to opacity of the label). Worked best with foil label as it was sufficiently opaque to allow the writing on label side to show through on the data side.