[Samba] Windows refusing samba server

[markus]

Hi, I have some issues with some windows machines (xp pro, 2003). It
sounds very weird, but some of my machines are loosing the connection to
my samba server. You can't see any machine browsing the network, it asks
for a password getting access to a samba share, which leads to a refused
connection. After this it asks never again for any password, just
refusing me. I can ping the samba server, but the client doesn't show
any shares, just talking about it could'nt find the specified host on
the network. The strange thing is, that everything worked very fine for 
months, since I encountered the first machine with these symptoms. A day 
later the next one. Than the servers, maybe earlier having these 
problems. And today another one.

I don't think that anyone encountered such strange and weird behaviour
on any windows machine. But every hint is very welcome.

Thanks
   Markus