Network problem cannot access certain shared network

I am working in an internet cafe and I'm always accessing files, from other Computers. Then suddenly one day, one of the units is inaccessible. I've checked the connection wires; checked the sharing folder, it's all ok. But still this problem occurs.
Workgroup
\Pc8 is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions.
The network path was not found.
OK
I already set up everything for this, since the start of my business. Can anyone tell me how to solve this issue please.
Thank you.
