Networking 4 PC's w/ Internet Connection(cable)

Previously I had 3 PC's on my home network, 2 running WinXP Pro, and 1 running WinXP Home, which were connected to a Motorola SB5101 Surfboard Cable Modem through a 4-port Linksys router. Everything was running perfectly; fast/reliable LAN and Internet speeds.

Recently, I added a 4th PC running WinXP Pro x64. Upon first connecting the new PC to my router, it got no "Limited or no connectivity," while my other 3 PC's were running perfectly on the local network and internet. So I shut down all 4 PC's, along with the router and modem. After restarting everything, the new PC was the only one working correctly on the network with the other 3 PC's receiving "Limited or no connectivity."

Since then, I've only been able to get 1 out of the 4 PC's on my network at a time. I can get any 1 of them working fine, but no more than 1. 3 out of the 4 always get "Limited or no connectivity." I'm fairly sure that it isn't the router, as I have tried 3 routers(2 linksys and 1 Asante) and have the same problem every time. I'm assuming it isn't the modem, as it works perfectly with any single PC, unless it suddenly decided not to accept more than 1 PC?

I've tried release/renew on any of the 3 PC's getting "Limited or no connection" and it always times out with "unable to contact your DHCP server" while attempting to renew, tried resetting the modem and router (along with the 4 PC's).. I haven't tried static IP's, as I'd much rather leave it automatic.. Any ideas?

Thanks,
Dan

if you remove the xp x64 pc, does the problem persist?

Yeah, it does. I can get any of the 4 PC's on the network (including the XP x64), but only one at a time.

if the xp x64 machine is causing the problem, then try replacing the nic. maybe it's doing something weird.

I thought it was the x64 PC at first, but when it's not physically connected to the network, I can still only get 1 PC working on the network at a time.

maybe your router is going belly-up. try updating it to the latest firmware version to see what happens.

I've tried 3 different routers.. but I'll try the latest firmware for each.. nothing else working :/

are you near any devices that can give off high levels of emi, like a microwave?

Nope. I have one large room with 3 PC's (and the router/modem) and a stereo, the stereo, sub, and speakers being mounted on the back wall not near any of the pre-mentioned hardware, and a 4th PC alone in another large room.

try resetting window's tcp/ip stack. open a command prompt and type:

netsh int ip reset c:\resetlog.txt