I have an Asus P5B motherboard but I have issues with the onboard Realtek RTL8111B LAN. All LED lights are functioning normally, all adapter drivers are installed successfully. However, there is no connectivity with the network.

I am running WinXP Pro SP 2 and have installed the Realtek drivers that came with the motherboard. I have even tried the latest drivers from the Realtek website. Firewall has been turned off.

I have 4 other PCs and they all connect fine through wired connection.

Here's how I've set up for the PC with the Asus P5B. Only Setup 3&4 appear to be working. My target setup is Setup 1.

Setup 1 connected to Linksys WRT54G:

PC connected to free port on Linksys WRT54G cable router. PC cannot obtain a connection either through DHCP, or specifying a fixed IP address and gateway. I tried ping from the router and from the PC and they cannot see each other. All other PCs on the network are OK.

Setup 2 direct connect to cable modem:

When I connect to my cable modem directly, I am able to obtain a DHCP but am unable to ping any of the DNS servers. The only thing I can do is FTP files from the local server on my ISP. I do not have issues pinging the DNS servers from my router and from my other PCs.

Setup 3 using a 10baseT hub:

When I tested on a 10baseT hub and set 2 PCs with a fixed IP address, I am able to ping each other and transfer files.

Setup 4 direct connection between 2 PCs with crossover cable:

This has the same effect as Setup 2 - no problems.

Any help is greatly appreciated.

3 and 4 show the network is fine. You did post a lot of info but not enough. Repost on new thread and show results what help and support pages "network diagnostics" show maybe.
It could be that you are using a flimsy cable or a crossover cable. Most modern ports auto negotiate but not all. Realtek's are pretty standard but not always 100% foolproof.

Put the known working computers cable into the suspect one and boot up the computer with the same network settings as the working system.

Keep the firewall on at all times!!!!!!

I read it wrong and answer it wrong too. So get off my case you goober.

I hooked a hub in between the router and the PC and that solved the problem. I am able to connect to the Internet as per normal (with the Firewall on of course :)) It can't be a problem with the cable because:

a. The daignostics tool show the physical cable is operating normally.

b. I am using exactly the same cable with and without the hub.

c. I have 5 cables at my disposal. They all work with my other PCs but not this one if connected directly to the router.

The problem seems consistent as the PC can only connect through an intermediate device such as a hub or a cable modem.

It's bizzare as the hub is a layer 1 device which only relays packets.