I've got several PCs connected to a FVS318 router, and have one pc that is giving me a problem. This pc is located in a building next door to the building that contains the router and is connected to the router by a 90' chunk of cat5 cable. The pc is the same make, model, vintage, OS, as all the other pcs that work fine. Configuration is a FVS318 router attached to an 18 port switch. All PCs are connected to the switch. The problem is that when I plug the problem pc into the switch (like the rest of the pc's), it won't surf, download email, etc. But when I plug it directly into one of the open ports on the router, then the pc works great. Any thoughts? Cable show to be connected correctly...

First thought is you have 17 pcs connected and you are trying to use the uplink port to connect the problem pc. Did you try other switch ports? Used the same cable for both tests? What is its ip address when it doesn't work? Ip address when it does work?

Not using the uplink port...made sure of that. IP address is the same either way (router or switch). Tried other ports and still the same problem...when plugged into the router, can surf like crazy. Plug it into the switch and it shows still connected but no speed. As for the cable, I have a 50 pair phone cable that connects the two buildings, a punch block on both ends and then cut a cat5 cable in half, and punched it down onto the block. I'm assuming I have the wires connected correctly as it works fine with the router but not the swich.....

Cat 5 cables are not made to be split. It should be a separate run. The change in capacitance and noise is killing the signal. The router port may be better than the switch.