2 computers 2 cable modems 2 cable connections -- both can't connect

Daughter & boyfriend blended households.  2 computers, both running WinXP.  2 cable modems.  One computer in living room, one computer in bedroom.  Cable connections in both rooms.  Both cannot be on internet at same time.  Any reason why?  I have set up a wired network at home using linksys and assume I can set up a wireless network for them by installing wireless in the older computer and purchasing a wireless router but wanted to make sure the current set-up is impossible before spending any more money.  They're both college students, therefore POOR!  Any help would be appreciated.
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Both cannot be on internet at same time.  Any reason why?
Are they trying to access the internet via a shared AOL account?
jstongAuthor Commented:
No  apparent reason.  When they first hooked the second computer up in the bedroom, it could access the internet.  The next day it couldn't.  They called the ISP (Cox Communications) and were told they would have to have a network set up.  Is it possible that when service was disconnected at the first house, Cox de-registered or unauthorized the modem itself?
Is it possible that when service was disconnected at the first house, Cox de-registered or unauthorized the modem itself?
That seems likely, in which case a router would solve the problem.
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I can't recall the details, but I believe that the cable companies set up the home access to go to one system.  Routers get around this by being that one system, and then distributing the packets to the individual computers.  

Try turning off both computers and unplugging both cable modems for at least 15 minutes.  This should reset the connection.   Then turn it back on, and see if the modem is working again.  

If so, the next step is to install the router... ;)
AntonioP has the right way to fix this and here's the details on it.

On the cable connection the Cox system is only going to allow 1 modem on there at a time.  This is because their system will use the MAC address of that modem to initialize on their network.  For the purpose of setting this up you should use whichever modem is currently working on the connection so you don't have to wait on the other to initialize.

Next get yourself a router of some sort.  Personally I use the Linksys series (common) because they are relavtively inexpensive even with wireless as you are looking into doing.  Setup the cable modem to connect to the WAN or Internet port on the router.  If you are using a static IP address you'll need to log into the router to set that up (default IP is with a username of admin and a password of asmin).  From there connect the wired PC to the router.  Most of the newer routers will have a 4 port switch built-in so it doesn't matter which one you use.  While you're in the router it would be a good idea to go ahead an configure your wireless network settings.  The manual with the router gives good instructions on how to do this if you're new to it.

Next if you're going wireless on the 2nd PC then install a wireless NIC and put it close enough to the route to make sure you have connection and configure it for that node.  Then from there place that PC anywhere in the house where it can get a good signal and you're good to go.

A couple of things to note is that the router will be configured to assign IP addresses to both computers so you can either set them up with static numbers on the same IP scheme as the router or you can just leave them in default to acquire their number from the router.  Either way works just fine.

The beauty of this setup is that you can keep adding machines to that same connection and you don't have to pay Cox another penny above their monthly fee for multiple PCs.  They really try to milk people for as much as they can by telling them they have to pay for multiple machines.  Let your router be the one point of contact and you're good to go.

As far as money on this setup you're looking at about $85 or so for the wireless router and around $45 or so for the wireless network card.  They'll be cheaper here and there but those are pretty good ballpark prices.

Good luck on the setup.

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jstongAuthor Commented:
Thanks everyone!  I guess I probably already knew the answer but was sure hoping there was some kind of work around (i.e. no money involved)!  ozo basically had the right answer but left me feeling as though there might be other possibilities and I really was looking for something definitive so I awarded him 25 points.  AntonioP validated Ozo but took it a little further which was making me feel more comfortable about the route I was probably headed down so I gave him 25 points.  willc88 went that extra mile so I don't feel as though I'll have to come back and ask too many questions about the wireless hook-up so I awarded him 75 points.  willc88 also spoke with apparent knowledge specifically concerning the workings of the Cox network and I now have a better understanding of what is going on.

Thanks again to everyone.  Love this place!
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