Hi,
Let me know how are the computers connected. Meanwhile I would suggest you to try these steps:
1) To check if a third party application is a cause, follow this link (http://windows.microsoft.com/en-us/windows7/Advanced-startup-options-including-safe-mode) for this Boot to the desktop in Safe Mode with Networking option and check if this issues still persists, if the issue is resolved, you need to perform a Clean Boot by following the steps mentioned in the following KB article to narrow down the exact source and isolate it: http://support.microsoft.com/kb/929135
Note: After clean boot troubleshooting step, follow the “Steps to configure Windows to use a Normal startup state” in the provided link to return your computer to Normal startup mode.
2) No firewall or security software blocks sharing
The issue may be caused also by your security program such an anti-virus or a Windows Firewall /Defender which might have conflicting settings as to not to perform certain tasks. I suggest that you temporary disable the anti-virus and firewall and check the result again. You would need to turn on the security programs again which you had disabled.
Important Note: Antivirus software can help protect your computer against viruses and other security threats. In most cases, you shouldn't disable your antivirus software. If you have to temporarily disable it to install other software, you should re-enable it as soon as you're done. If you're connected to the Internet or a network while your antivirus software is disabled, your computer is vulnerable to attacks.
3) Password Protected: OFF (unless you want to set up identical usernames and passwords on ALL computers in your Network) or you can try creating the same username and password on both the computers.
Try pinging IP address of the computer from the other but not by machine name (PING each computer by IP address, and if successful, PING by name. You can obtain the IP address of a computer by opening a command prompt (DOS window) and typing IPCONFIG)
4) Ensure NetBIOS over TCP/IP is enabled on both computers
i) Go to “Control Panel - Network Connections”.
ii) Right-Click on the connection and click Properties.
iii) Find Internet Protocol (TCP/IP) Version 4 in the list.
iv) Click Properties, and then click Advanced.
v) On the Advanced TCP/IP settings windows, go to “WINS” tab.
vi) Under NetBIOS setting, click Enable NetBIOS over TCP/IP, and then click OK.
5) Disable IPv6
If the issue persists due to IPv6 deployed you might need to follow the steps mentioned in the KB article: How to disable certain Internet Protocol version 6 (IPv6) components in Windows Vista, Windows 7 and Windows Server 2008
Reference KB Article link: http://support.microsoft.com/kb/929852
Also check the following links for more information on networking:
Choosing a network location
http://windows.microsoft.com/en-US/windows7/Choosing-a-network-location
Create or modify network profiles
http://windows.microsoft.com/en-US/windows7/Create-or-modify-network-profiles
Add a device or computer to a network
http://windows.microsoft.com/en-US/windows7/Add-a-device-or-computer-to-a-network
Hope the information is useful.