It sounds like some configuration error or virus problems. As configuration part have u configured the Guest Access area and the Deny Access ….. option in Administrative Tool.
If they r all okay , then u try to scan ur computers with good Anti-Virus and always update them with patch. I experienced the same problem, it was virus problems…..
And also check the LAN ports and NIC of all computers if necessary repair them also !
Doesn’t sound like anyhting virus-related. Seems the shares and permissions on the servers/ PC arent setup properly..