I have three computers on the LAN in my apartment, all connected to an ethernet router- one running winxp, the other two running Ubuntu 9.10. One of the two Ubuntu machines is brand new (it's running 86 64-bit), and yesterday I transferred a bunch of files from my old Linux machine to my new one by sharing the home folder of the old one and then accessing them via the network on the new one. Today, when I go to places>network, the only thing that shows up is the windows network- whereas yesterday the name of the shared folder from the other Linux machine was there as well. Plus, when I click on the windows network icon, I get the message:

Unable to Mount Location
Failed to retrieve share list from server

Please help, and keep in mind that I know very little about networking, so if you have a fix your instructions will need to be detailed.
Thanks.