Make sure that the cable is not loose. if possible check the network card.
and if it is still so then you have to check the network service.
Click start -> run -> type services.msc
Which will be the last in the list of services.
Make sure it is running else start the service.
I am using kaspersky antivirus. When i close it sometimes it asks whether to close the open network connection and i use to give yes.
It closes gtalk and other open connection which i was not aware.
May be it would have stopped the network service also.
So when i checked using services.msc it has been stopped but not sure whether it is because of anti virus.
Anyway, i started it and i could browse the local area network computers.