Vista - Computer are online but can't ping each other

I have 2 computers attached to a linksys router.

The computers are online but can't ping each other, and I can browse the other computer and access the shared files.

Under sharing and discovery on both I have
Network discovery on
File Sharing on
Public folder sharing on
Password Protected sharing off

Do you know what I need to do?

Make sure you have both PCs set to allow full administration access across the network, about the only thing I can think of right now but my brain is fried from a 10 hour day.

Thanks! How do I check that?

Sorry I am a newbie

If you cannot ping, check if the name of the network is the same on both computers.

Yes, they are in the same work group. They are showing up in network, but when I double click on it, it says Windows Cannot Access \\COMPUTER2

When I click more details it says:
Windows sent the request to the DNS server and the server responded that the name was unknown.

Why is it checking a DNS server, that is a local computer name?

Do you use a firewall? Have a look a the network setup.

Yes, and you are right, that was the problem.

Thanks