do you have youre original network card back in the machine? sometimes ISPs
connect directly to your modem by MAC address or if they have problems
your NIC..
you may have problems with your layout.. double check to make sure that
your new goodies play nice with your old ones and that you are using the
right type of cables. really scrutinise the connections and make sure the
color patterns match on each end of them. make sure the new components
are auto sencing for 10/100mbps
dont forget you may have to change your default router in your network
settings if youve swapped out components..
when in doubt, diagram it out.. no one will ever chastise you for walking yourself
through on paper.
If youre still stuck you can always hurt a live technitians head from your ISP as well.