Let say I've got a computer in one room connected to one data jack (RJ45). If I take this computer and put it in another office, hence another jack, it'll be unable to connect. Our network is pretty simple. We use DHCP with lease duration of 5 days. The PDC is a WinNt 4 Server with Proxy Server 2.0. The clients are Win98. I did all the regular tests to see what was the problem... ping, Find --> computer, reinstalling NIC, deleting the lease in DHCP manager, etc. This happens with only a few of the computers in our network (oldest ones). They all had fresh installation no more than a year ago. If I take back this computer to its original location, it won't connect back. I knew it might have to do with the server, so I tried to connect 3 days later and then it work! But if I move the computer again... nothing. I even tried to install winsock proxy client on the computer, which shouldn’t really matter, but hey, you never know! There is something odd thought; if I make a release all and then renew all in winipcfg, It'll give me the right ip, subnet and gateway. So I believe its communicating... but why can't I ping (request timeout) or view servers in network neighborhood.

Sounds like you tried a lot. Is it only particular ports that the PC's won't connect to? Check the configuration on the ports (on the switch). Verify the DUPLEX and SPEED of the port and check if the NIC cards on those old PC's can handle it. If you can get an IP though that's odd. Are you positive that the network info is correct (i.e NETMASK,IP,GATEWAY). Are you sure the IP you are getting is from the right DHCP server? The port that you move to is it on another switch? Are you sure that what you are pinging is a valid hostname or IP address? Just some suggestions, good luck.

Thanks for the suggestions Marcos but yes, renew all gives me the right IP, gateway and subnet. We one have got one DHCP server Mathieu

There could be many things going on here. First try releasing the address ON THE WORKSTATION before you shut it down. (Run WINIPCFG and click release all for those of you that don't know how to release the IP information.) There could also be network config problems with the hub/switch. Are you running a 10/100 MB switch? If so, what is the switch set to do about speed and duplex. Only the SWITCH or the PC should be set to AUTO CONFIG the speed. Try going into the network card properties and setting the speed to 10 MB and half duplex (all ethernet cards can handle this). Confirm the computer still connects properly. Move the ocmputer to a different location. If it works, you have a handshake problem. We are in the process of swapping out all of our 3Com 10MB hubs for Cisco 10/100MB switches. There are some PCs that have NICs that can only communicate at 10 MB half duplex. Therefore we set all of the ports to 10 and half on the switches (by default) and only modify ports on the switch when we know the machine can handle higher speeds. We usually let the PC figure out the duplex and speed on the machines with better NICs. Still, there are computers that will not reconnect to the new equipment unless we modify the NIC properties manually. Some cases we put them back on 10 and half just to get them to work. The real strange problem with some of these machines is they will get an IP address but won't talk! IPX works just fine. We change the NIC speed to 10, and change the duplex to half (instead of leaving it AUTO DETECT) and the machine starts working!