I need help with a ping problem

I have 3 computers connected to a router. All have perfectly working internet access.

2 of the computers can not be pinged but they both can ping the third computer. What steps can I take to troubleshoot this. I'm not sure what to check with the firewall and etc.

The computers are Windows 8.1 (can be pinged) and the other two are Windows 7 pro (can not be pinged).

Since 1 computer works correctly, I left the router at its default config, so I assume I have to configure Windows 7 somehow.

Any help would be appreciated and if you mention your troubleshooting steps, it would be immensely helpful for me in learning.

Thank you!