I think you need to explain yourself a bit more.
Are you trying to move the ethernet cable that comes from your modem from your PC to your laptop?
If so, your laptop may have a connection for a phone line modem AND an ethernet connection.
Make sure you are not trying to plug your ethernet cable into the socket that is for your modem, they are very similar.
The ethernet socket on your laptop should have this small icon next to it
http://www.housing.wisc.edu/resnet/images/rj45 -1.jpg
If you are NOT trying to move your ethernet cable can you explain what you ARE trying to do.