After turning the router off and on, no network connection

hi,
I have two win7, two win xp (4 in total) connected as file sharing network.
1. When I turn the router off and then on, the win xp computers see all the rest, but win7 computers see no one, they still have the internet ability.
2. If I turn on the win7 computers first: the 1st sees nobody, the second sees the first but not the consecutive computers. No home group.
what is wrong here?

thanks ahead,
Manni

This link should help you get your network set up properly for sharing between your XP machines and the Windows 7 machines. After going through this procedure if you are still having problems there are a couple more things we can do with the security permissions to get it working.

Share Files and Printers between Windows 7 and XP - How-To Geek

Thanks for the reply. I did all that before. It works fine as long as no interruption at the router or when turning off/on the win7 computer. I am going tomorrow away, and be back on tuesday.

Try this tutorial: http://www.sevenforums.com/tutorials/53830-file-sharing-between-xp-w7-vice-versa.html