well if your prepared to throw it away, no harm in having a lookin, If the
modem is still talking to the pc indicating the cpu ram psu etc... is
working it might even be easy.
Im sure there are a lot of more knowlegeable ppl about on the subject, but
typically there are just a few caps and a transformer that interface to the
phone line, these are your first suspects. From thereon your probably
looking for fried IC's, and I would hesitate to replace IC's due to cost and
time.
Again it depends on the symptoms of the modem. I would really only consider
it possibly fixable if it powered up and communicated with the pc ok, but
couldnt get line sync.