How to solve problems with MS Windows network?

Question

Windows

There are 2 computers on the network, S and M (on both WinXP), and a media attachment W.
Both computers have shared folders. All three devices are connected to the router via ethernet.
At some point, suddenly, the prefix W stopped seeing computer M.
The investigation found out the following: computer S is visible
from the console.
From computer S, computer M is visible in the network environment, and the prefix W
from computer M is visible only computer S in the network environment.
That is he does not see himself!
Question. What the hell and how to fix it?

Answer 1

Magically, the problem disappeared by itself. So I didn't understand what it was.