Computers connected on LAN ports, via a wireless router, are unable to communicate

What I have

Linksys WRT54GL with DD-WRT replacing the original firmware
Linksys is connected to the internet on the WAN port, standard stuff
2 windows (7 and 8) desktop computers connected via the LAN ports (2/4 ports consumed)

What doesn't work

Any server application, running on a computer that is on a LAN port, isn't able to be connected to from inside my home network (eg: one computer is not able to ping or ssh to another if it is on a LAN port).
Update: doesn't seem to matter if this the client/server is wireless or LAN.

What works

internet on all machines, wireless and LAN connected
ARP. I am able to type arp -a after running ping ip-to-LAN-connect-computer and I see the MAC address added to my arp cache.
I can ping my router via ping 192.168.1.1 and that works from both PC's.

Troubleshooting so far

windows firewall is off. AV firewalls are off.
Being able to ping/connect worked before when I had this router and these computers at another place about 5 months ago.
For DD-WRT settings... I did a setting reset. Then I set... SPI firewall: off

Here is my routing table:

Destination LAN NET, Subnet Mask    Gateway, Interface
192.168.1.0          255.255.255.0  0.0.0.0  LAN & WLAN
x.x.x.0              255.255.255.0  0.0.0.0  WAN
x.x.0.0              255.255.0.0    0.0.0.0  LAN & WLAN
0.0.0.0              0.0.0.0        x.x.x.x  WAN

notes: omitted with real IP's with x.x.x.x for security

It sounds to me like your computers are sending icmp but not answering icmp. Ping replies on windows 7 are automatically allowed if port 445 is accessible.

You can confirm this by getting a fourth device and pinging to the router and both computers. Or by pinging from the router to the computers using the router interface.

Check the firewall settings on the router. Turn off the router firewall and disconnect it from the internet if you want for security reasons while you test ping.

I am guessing your router is doing something such as:

Filter Internet NAT Redirection This feature uses port forwarding to block access to local servers from local networked computers. Select Filter Internet NAT Redirection to filter Internet NAT redirection. This feature is not selected by default

http://downloads.linksys.com/downloads/userguide/WRT54GL_V11_UG_C-Web.pdf

Try this if it exists. go to the Networking Properties of the connection from Control Panel\All Control Panel Items\Network and Sharing Center and turn off AGN Filter Interface (64-bit).
- Check if you have installed any networking software from isp's for example and remove it.
- It seems possible that something happened to both your computers at about the same time for them not to answer icmp. Try turning on your firewall again and explicitly re-enabling icmp. Check for redirected ports. Make sure the settings are permanent by closing the window and re-opening it.

I don't know if this could be the problem but it's better to mention it than to leave it out.

Make sure you have enabled Network Discovery.