Help: DNS server unavailable

[zulu9812]

Alright, I have a tricky one.

I have 2 pcs networked together via a gigabit switch, the gigabit switch is then plugged into a cable modem (router). The modem router was replaced by the cable company today, promising a doubling of my internet speed. Yay, I thought.

But only one of the PCs is actually connecting to the internet. Both are running Windows 7 Pro. Computer A is in the same room as the router, but is still connected to the switch and the switch is connected to the router. Computer B is in the next room, with an ethernet cable running to the gigabit switch. The cables running from the PCs to the switch are cat6, whilst the cable running from the switch to the router is cat5e.

So far, fixes I have tried are:

hard reset the router (i.e. unplug power cable for 30 seconds)
hard reset the switch
unplug both the router and the switch, reconnect the switch, then reconnect the router
swapped the cables that run from the PCs to the switch
ditched the switch altogether and connected both PCs directly to the router
ipconfig /flushdns, then ipconfig /release, finally ipconfig /renew (/renew wouldn't work because command prompt said that it couldn't renew whilst the media was disconnected)

With Computer A, I can swap the cables around, do hard resets of the router and switch, etc. and the internet connection always "takes", without having to reset that PC. I've restarted Computer B god knows how many times and it just won't work. The network icon in the status bar says "internet access" but when I try to browse in four different web browsers (opera, firefox, ie and steam) I get "server unavailable" errors. I've also tried to run update programs (such as my ASUS bios software) and they don't connect either.

I'm tearing my hair out here. Can anyone help?

EDIT: I was able to configure my 'phone to access the router's wifi. So I'm pretty sure that the problem is with Computer B itself.

 

[timtofly]

Did both computers connect before today?

Can you see both computers on the same network?

Do you get any indicator lights where the cables plug into all ports on the computers and the switch?

Can you log onto the cable modem (router) and configure it?

What was the reason for the modem change?


Thoughts:

There is a hardware problem with the port on computer B. New network card, or motherboard.

The new cable modem has been configured to allow only one connection.

The switch should act as the one connection that the cable modem can only view. If the switch can see both computers and both computers can see each other and swap data, then perhaps there is still something with the new modem that is blocking the ability of the switch, and that does not make any sense.

Using the switch acts as a firewall, that you can control. I am not sure that using a modem from the cable company, even as a router, will give you that firewall, as the cable company is not going to give you total access to their network, and their modem is another node on their network, and it is their buffer between your network and theirs.

The bottom line is to get your network talking to each other via the switch, and if that works, then connect the switch to the modem and go online. If your computers are not connecting to each other, then the issue would be with the hardware of computer B. It does not make any sense that if it worked before, that some software change happened to lock out the one computer. My guess is that the old modem may have been more forgiving on what connected to the internet, and now you need the switch to get your network to act as only one connection. Or there is a hardware issue with Computer B.

 

[Zelig]

What's the IP address on computer B, computer A and the router? If you log onto the router's admin page on computer A, does computer B show up with its IP address?

 

[zulu9812]

Thanks for the replies guys.

In the end I went to Local Area Connection Status > Properties > Internet Protocol Version 4 (TCP/IPv4), saw that it was set to use a specific DNS server address and changed it to acquire an address automatically. And now it works. Weird, I don't recall making that setting originally. Anyway, I learned something new!