I've run across this problem on multiple sites.
Typically a win 98 pc connected to NT4 server and using
a shared printer via peer-to-peer Microsoft networking (tcp/ip only ) reports they cannot print. They were running along fine, when out of the blue all access to peer-to-peer has disappeared. Their server mapped drives are still present and working but attmpting to browse the network shows that all other connections are unavailable. Reboot and all is well...for a while.
I've replaced the NIC, tested the cable, searched for updates, even replaced a PC but with some regularity (every few days typically) the problem recurs.
A sight variation occurs with a Novell server where the server drives also become inaccessable as well. In that case the problem seems to occur at startup, after sometimes several re-starts all is well till the next day.