You have drives missing? As in what? Two CD-ROM drives gone?
If there's two drives both gone at the same time, it's pretty unlikely that they would have both worn out at the same time. Like Danny said, try changing the IDE channel, if you reckon you're up to it. In these cases, Knoppix is an invaluable tool. Basically if you run Knoppix (Linux-based OS that boots directly from a CD), and can access your drives, it's a problem with windows (I.e. software), whereas if that still has the same problem, then it's a hardware problem most likely.
However, if your CD-ROM drives are fooked, then you might have trouble booting Knoppix :o
Linky - About a 700mb download - OK if you're on broadband. But again, you might have difficulty burning it to CD if your drives are broken. Maybe you should download it on another PC :o