Home Network Stopped Working

If the symptom is always that plugging in the second computer makes the first lose internet connection, and unplugging second computer again gives first computer's connection back, that should narrow it down some. If this is what happens, is it also what happens if you swap which computer you call first and which second?

I have a wild guess at this point. Could the two computers be trying to use the same network address? Probably it would be the IP address of the eth0 devices on each machine, as shown by running ifconfig in a terminal on each machine. Or look at "connection information" in the right-click menu of your Network taskbar icon, if you've got such a thing.

Thanks, Paul. Your wild guess could be the answer, but I am not computer savvy enough to know. Here is what I found:

wired connection (eth1)
address dhcp

wired connection (eth0)
address dhcp

modem connection
this network interface is not configured (???)

I don't know why it says the modem is not configured, or what that means, but the modem is working because I have access to the Internet.

I also have two DNS servers listed. What is a DNS server? Is it important for this problem?

Oh, I see that you ask for the address on each machine. What I posted above is for the first machine.

I cannot easily move the 2nd machine to the location with the modem and router and hope to try to figure this out without needing to, if possible.

Since we had a power outage here today, I had to reboot my computer and it had to go through a memory test. The 2nd computer is still down. I will come back to this when I have the additional information.

Meanwhile, does what the first computer show (above) help shed any light on this?

My wild guess is that internet router is failing
"I can tell my system is failing when the green lights on the router start flashing on and off, sometimes sequentially, sometimes randomly. The modem activity light blinks. I receive a message on my screen saying that I am disconnected from the network. And then neither computer has Internet access."

But before wild guesses, confirm is this is your setup:
You have 2 computer on different rooms connected directly to the internet's router by cable
I have read that you have a switch, where is connected?

Well, the 2nd computer came back from the power outage, and after I got my son to log in with his password (unknown to me), I tried to find out the Internet address, and couldn't. I went to System, Network or Networking, and then it asked me for an Administrative Password.

My son and I don't know the password because my ex set that up. I have tried to reach him to request it, but he has not answered me.

The Set Up:

The first computer is connected to both the modem and the router, which are located right next to the first computer. The router is connected to a switch by a cable that goes through the ceiling of several rooms, ending up in the basement near the furnace (not that that should matter). It's been there for years, working fine.The switch is then connected to the 2nd computer by another cable going through the ceiling.

It would be difficult to try to connect the 2 computers directly because there is nothing in the ceiling to allow me to pull the cable through. That's why I have the cables going to the switch, which was the original setup.

I have replaced the switch, the cables, and the ethernet interface card in the 1st computer.

After replacing the cables, I tested the old ones and found that they were working fine. I took out one of the new cables and reinstalled one of the old ones. I am hoping that it does not matter if one cable is CAT 5 and another is CAT 6. If it does, I can take out the CAT 5 again and replace it with the CAT 6, as I have learned it is not returnable without a huge restocking penalty and shipping costs both ways.

First, I recommend not buying any more equipment, as based on your reported symptoms it sounds a lot like a configuration error.

Please right-click on the network icon that appears on your taskbar. You should see a "Connection Information" option. (You will not need any administrator privileges). Select that option, and please note the following information:

Interface:
Hardware Address:
IP Address:
Broadcast Address:
Subnet Mask:
Default Route:
Primary DNS:

Please include this information in your updates. It will allow me (or someone else vieing this report) to determine whether a duplicate address or network misconfiguration is causing you grief.

Also, it is important to obtain your Administrator Password as soon as is realistically possible. Without it, you will likely be unable to fix other errors that could occur over time. You may also be unable to make network changes, should they be required.

Please repeat the above for both computers. Thanks.

Thanks for the help. Here is what happened:

Over the weekend I removed the new interface card and the switch and connected the 2 computers directly by a single CAT 6 cable.

I purchased a new router and installed it.

The Internet is working fine on both computers now.

However, I have also retrieved the Connection Information as indicated in the post above. I don't know what it said when there was no Internet on the 2nd computer, but now that the initial problem is resolved, the 2 computers are the same on everything except:

Driver, IP Address, Primary DNS, Secondary DNS, and Hardware Address.

I understand that the IP Address is correct to be different. But I do not understand the Primary and Secondary DNS, the Driver, or the Hardware Address.

On the 2nd computer, the Secondary DNS is all zeros: 0.0.0.0

Is this something to be concerned about?

What does DNS stand for?

What is a Driver?

Also, when trying to figure out what was wrong, I attempted to run my computer without the old router, using just the modem. My computer was not connected to my son's computer at the time, as I was trying to simplify things and see what would happen.

With just the modem, my computer could not access the Internet.

That just seems weird. I wish I knew why the modem alone would not be sufficient. The modem was working fine, and the lights were lit up, as normal. However, my connection to the Internet did not exist without going through the router.

OK, thank you.