Can you please post the ipconfig /all output of both computers?
What happens if you temporarily disable the Windows Firewall?
Can you try accessing the computer by typing the IPAddress? Click on the Start button then type \\IPAddress\Shared Drive or Shared Folder (example \\192.168.1.10\TestFolder)
Also, make sure that from the troublesome computer verify that all your network services are Started from Control Panel=> Admin Tools=> Services:
• COM+ Event System (for WZC issues)
• Computer Browser
• DHCP Client
• DNS Client
• Network Connections
• Network Location Awareness
• Remote Procedure Call (RPC)
• TCP/IP Netbios helper