lost network connection after installing winxp service pack 1

need help asap. Installed winxp on my son's pc. everything was working
fine-had internet and email through a network with linksys router and dsl
modem. then installed service pack 1 and lost my network connection. It
shows the connection and other computers on the network but cannot access
internet,mail or shared folders. If I un-install service pack 1-it works fine
again but then cannot run certain programs like itunes. Need help asap
leaving soon for military deployment overseas and need to have fixed before
I leave !!
.

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