CD/dvd drive not found

Dell Dimension B110, running XP, SP3
CD/dvd not working and computer cannot find the drive - BUT - only if
computer is booted up with the broadband internet cable attached and it takes
forever to boot up, probably because the computer is trying to find the
drive. Once the computer is fully booted up (without the CD/dvd drive
function) the internet connection works fine.

However, if computer is booted up without the internet cable attached, it
boots up quickly and everything works fine - including the CD/dvd drive.

So - we can either have the CD/dvd RW drive OR the Internet connection, but
not both.

Don't know if this has anything to do with it, but this is my son's computer
and he had not opened up the case and blew the dust out since he bought it,
so when I opened it up, I found a "blanket" of dust over the air intake and
dust balls the size of golf balls rolling around inside the case.