need help with LAN connection problems, network driver installation, etc.

Only one computer, local area network, LAN.
I tried what is told in the question. I tried to install my network driver as a possible solution but I ran into a dead end in the LAN folder, since I do not know what to do to "install" the network driver. There are files in that LAN folder but no "install" or setup files that I can see. Tech support for my ISP suggested 3 possiblities:
1. install the network driver
2. their cable modem could be bad
3. take the pc to a repair shop since a bad modem would not cause me to be unable to disable the LAN connection. I'm not able to disable the LAN connection to continue their tech support. They only handle their end of problems, and they imply, since my system won't let me disable the connection, then the issue is with my system.
Everything was fine and a couple bootups after the monitor exchange no connection. But, they say that can not be the problem, justa coincidence. They've tried to tell me all they can for what they are paid and allowed to do.

You say right click on NIC. What is NIC?
Network Internet Connection?

Mine is a local area network 3.
On the computer I'm using to be here now it is LAN 2.
Can you suggest what I should see in protocol?
(since I can not be on both systems at the same time - one or the other)

Yes yours is  local area network 3.
You should see (probably on the bottom of the list) Internet Protocol (TCP/IP)
Protocols are the ones that have the same symbol as the Internet Protocol (TCP/IP)

The Vista machine is using the same source to access the web.

I took the XP machine to a shop, and free diagnosis. It connected to ISP like normal.
They said they see maybe one of these issues a week. They suggested that what was wrong was the Toshiba Cable Modem or something related to the ISP, and not my system.

They could not explain my inability to disable the connection but they said it seems not important since I can connect, or I did connect at their shop.

I'll hook my pc up again and this time if it fails, then it is some ISP issue in my neighborhood, on my incoming telephone pole, etc.

It seems my system is fine except the ability to disable the connection.
And the Toshiba cable modem was able to access the ISP about 6pm Sunday with the Vista system, after failing to connect with the XP machine between 3pm and 5:30 pm before giving up and planning to let the shop take a look.

i doubt it'd be an outside problem with your isp if another machine can access it fine.

i'd recomend trying to uninstall the lan card from device manager as above, and re-installing it on next boot.

then try another ethernet cable and see if that could be the problem?

if another machine can access everything fine with same settings then it's not a problem with your modem or anything else bar the machine somehow imo.

I agree.

If it is an onboard nic, try disabling it in the bios, and either boot to Safe Mode and uninstall the nic in Device Manager (or use Show Hidden Devices in Normal Mode).
Reboot to Bios and Enable it again, and let it reinstall.
If that doesn't work, you need to try a new nic.

And the Toshiba cable modem was able to access the ISP about 6pm Sunday with the Vista system, after failing to connect with the XP machine between 3pm and 5:30 pm before giving up and planning to let the shop take a look.

I reported the above yesterday.

The issue seems to be an unknown problem with the ISP or the cable modem or other.
I replaced the Vista machine with the XP machine (today 7pm EST) and it connected to the local area network as normal.
I also noticed how slow my computer is to the newer one. It must be the processor and hard drive and not Vista...???

The repair shop said they get one like mine every week, so it seems an ISP problem of some sort.
My network card is almost 2 years old, so it could be a source of problems in the future.

Adding points and closing.

the repair shop implied a temporary connection problem with the ISP, during the time frame when I could not connect, so not a permanent thing.
It is the first time I've never been able to connect since having cable modem service, over 3 years.

awarding points based on the most definitive solutions offered and amount of info that can be helpful in the future. Accepted solution being the command prompt diagnostic action.