Here are few checklists to determine the root cause behind the Network Discovery failure.

1. Firewalls play a major role in Networking. As such, my first suggestion is to temporarily turn off any firewall or security softwares such as avast antivirus. If firewall is the problem, you'll have to change its configuration. If you need any help with it, please check with the software vendor.

Note that some firewalls must be completely uninstalled to stop them from affecting your networking.

2. Run ping command to test network connection.

Hold the Windows key and press R, then type CMD to open a command prompt.

In the command prompt window that opens, type the following command:

PING <ip address>  and press Enter.
PING <computer name> and press Enter.

Where:
<ip address> - is the x.x.x.x IP address
<computer name> - is the computer name

A failure to PING is almost always a firewall configuration issue. Any failure to PING needs to be corrected before you go any further. Once you figure out if firewall is the problem, you may choose whether or not to continue with this post.

3. Run the Network troubleshooter to see if it can help diagnose and solve your problem.

Open the Network troubleshooter by right-clicking the network icon in the notification area, and then clicking Troubleshoot problems.

4. All computers should be in the same workgroup for computer browsing to function properly.

5.  Make sure that computer is on and that you've enabled file and printer sharing on your network.

6. If you encounter difficulties accessing computers that are visible in Network Neighborhood, make sure the computer being accessed has an account with the same name/password as the system connecting to it.

7. Check your Services.
Ensure that the required services are Started on all the computers:
Sometimes they have not started Automatically -bb
Go to Start\Control Panel\ Administrative Tools\ Services.

       o Computer Browser
       o DHCP Client
       o DNS Client
       o Network Connections
       o Network Location Awareness
       o Remote Procedure Call (RPC)
       o Server
       o TCP/IP Netbios helper
       o Workstation

 All of these services should be started, and their startup type should be automatic.
To change the startup type, double-click on the service name and change accordingly.

This should do the trick.

For additional information on Networking issues, see this help article.

Why can't I connect to a network?
http://windows.microsoft.com/en-US/windows7/Why-can-t-I-connect-to-a-network

Note: Please turn on all your firewall and other security softwares installed after completing the steps given above.