When it stops working, I'd like you to check the network services.
Check your Services are Started on all PCs:
- Computer Browser
- DHCP Client
- DNS Client
- Network Connections
- Network Location Awareness
- Remote Procedure Call (RPC)
- Server
- TCP/IP Netbios helper
- Workstation
Note: You can check the services in Control Panel, Administrative Tools, Services.
All of these services should be started, and their startup type should be automatic (or perhaps manual).