Onboard ethernet can't see internal network

[videobliss]

I recently built a new computer using a Soltek SL-865PRO-775 motheboard that has built in gigabit ethernet. Everything about the computer works great, but I can't get the computer to see my internal network. I am unable to ping the other computers on my network from the new computer and the new computer can't ping any computer on the network but itself. I can connect to the Internet using the same ethernet port with no problems. I installed a fresh copy of Windows XP SP 2 OEM. Everything else on the computer seems to be working correctly.
I'm using a Belkin router connected to my cable modem (Roadrunner). Currently, both computers are hooked up directly to the router, though initially the new computer had a switch between it. IP addresses are assigned dynamically. The router is at 192.168.2.1, with my new computer currently assigned to 192.168.2.79 and my old computer set to 192.168.2.10.
I did try setting a static IP, but that didn't fix the problem.
Of further note, when I added the new computer to my workgroup, it refused to see anything on it, including itself.
Has anyone seen a problem like this or have any clue where I can begin to troubleshoot this?

Thanks.

 

[Micronaut]

Try setting the AutoSense in the NIC to 100 Full Duplex (some have issues)

 

[videobliss]

No, that didn't fix it.

 

[Micronaut]

So let me get this straight...

You're getting an IP from the router.
You can get to the internet

Assuming you have 2 other machines on the network, can THEY ping each other?

Print out an 'ipconfig /all' from both machines and paste it here.

 

[foxkm]

If the other two computers have XP on them with XPs firewall enabled then you won't be able to ping them. Make sure all firewalls are turned off on all machines since you are behind a router, there is no need for software firewalls.

KMF