I can't Log onto the Network

With so many components in the chain - NIC's, cables, hubs and OS drivers - troubleshooting network connections is never easy.  You have to approach the problem systematically.

First, check the obvious.  Make sure all cables are securely connected to their ports in the NIC and hub, link/activity lights are on, and all equipment is compatible (i.e., 10Mb per second NIC's with 10Mbps hubs, 100Mbps NICs with 100Mbps hubs)

A lot of equipment can operate at both 10Mbps and 100Mbps, so if the equipment doesn't autosense the speed, make sure you manually set it on all devices in the connection.  Some older autosensing 10/100Mbps NICs choose a speed, and are locked into it until you power down and back up again.  So if you manually switch hub speed from 10Mbps to 100Mbps and experience problems, turn off the machine with the NIC an turn it back on again.

The cable may be your problem, even if all link/activity lights are on.  Ethernet wires are crimped into RJ-45 jacks, and they can slip enough to break the connection.  Test them with an Ohm/Power meter set to indicate when there's continuity between the pins on each side of the wire.  This also helps you verify the wires are pinned straight through, not crossed.

If all's well on the physical side but problems still persist, use WINIPCFG.EXE (IPCONFIG.EXE in NT) to ensure the OS knows the NIC is operational, an that the proper protocols (IP/IPX and so on) are loaded and bound to the NIC.  NIC's that aren't loaded property won't show up here.  If everything checks out, use PING>EXE to test communications with other machines (preferably local) using TCP/IP, or with machines that are reliably up on the Internet (make sure you dial into your ISP first).

For instance, "ping ftp.somewhere.com" will report a series of "reply" messages with response time in milliseconds.  If you know the actual IP address (www.xxx.yyy) of the machine you are trying to reach, use that instead of the qualified domain name.  This eliminates the possibility of a faulty DNS setting.  If you don't know one, ping a server by name and ping will give you the IP address.

If pinging and IP address doesn't work, remove the NIC's network configuration entry and reboot.  Windows should recognize the NIC and reinstall it for you.  You may need to reinstall and configure  your TCP/IP protocol settings as well.