Laptop won't work on Network?

out of 3 work computors, 2 connected thru ethernet work good but the wireless laptop doesn't show connected to the shared workgroup. Although the internet works fine. All file and printer sharing enabled. When trying to add it to the network it shows Local Area Connection unplugged. It was working fine a month ago and wasn't connected thru a ethernet connection. Using Windows SP3 on Att router using DSL.
Suggestions appreciated!!<