LAN disconnection

My internet connection is ADSL via my PC's LAN port. This
was permanently on until a couple of weeks ago
(coinciding with the latest Windows XP update). Now my
network connection drops off after a while and the PC has
to be rebooted to regain connection. There is no problem
with my ADSL router as my wife does not experience this
problem on her PC in another room. I have tried all
available settings options within Windows without
success. Hope somebody can help me. Thanks.