What is your definition of not working? You can't see a computer, what? Please elaborate when asking a question. If you can't see a computer, try going to Start>Run and type:
\\*name of another computer on the network goes here*
If that doesn't work, then try configuring the ip address of the machines to either 192.168.0.x or 10.1.0.x where x is a variable. Make sure all machines on the network follow the same format or else it wont work. Also, check to see that the network card/hub/peer network card light flashes, if not then it must be a hardware problem whether it be the cable, the card, the hub/switch, the peer computer etc.
You may want to try going into command prompt/dos and typing: ipconfig
this will let you know if you are on the network or not, if it doesn't work it's a hardware problem. If it works, try pinging another computer on the network.
Basically what I'm saying is, screw around until you get it. Did you change the workgroup of your computer while you were away? Are you on a domain? If my advice hasn't been helpful, post back with more info.
Cheers,
Slade