Home network puzzle -- things have fallen apart.

I have three computers which until recently shared all their disks via a
wired/wireless home network. Recently the networks has gotten into a mess and I
haven't found out how to get it working again.

The situation:

Computer A has read/write access to the disks on computers B and C
Computer B has read/write access to the disks on computer A, but throws an
error "\\C is not accessible. You might not have permission to use this
network resource. etc."
Computer C can't even access the network, throwing an error
"Network is not accessible. etc."

When this first happened all machines had matching (name & password) users, with
full permissions set on all. (Note that it had been working, but machine C was
off-line for a while, and was used away from the house -- it is a laptop)

On advice I created new user ids, identical on all machine, members of the
administrators group, and set permissions from those. I renamed the machines
and the created a new workgroup. But the same behavior persists.

What is my next step on getting this sorted out????

Cyril N. Alberga