Lost Connection to Workgroup

I have a local network running among four computers. On one of these,

I have lost my ability to connect with other computers in its

workgroup. This had been working for ages and I'm not sure what could

have caused it. I can connect to the router and have access to the

internet.

My "network places" shows the workgroup, but when I click on it to

connect I get an error message that the workgroup is not accessible

and I might not have permission to use this resource. I've checked

that the workgroup name is correct and even went through the process

of re-entering the name - to no avail.

I appreciate any advice.