Linksys router no internet

I am trouble shooting a linksys router that my friend dropped off.  He said that he can't get onto the internet but when he plugs his laptop into the cable modem he can get on the internet

I have the same router (linksys WRT54g) so I started testing.  

1.  First I uploaded the latest firmware to his router.   did not help
2.  Reset router to factory defaults   did not help
3.  Matched his router setting to mine.
     B.  The only difference was on  the status tab under router, it is not obtaining a DNS, external IP address, or domain name.

Any ideas or recomendations?
HBMIAsked:
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cripplecaptainCommented:
Some modems will only allow 1 mac address connect to them, depending on the isp resetting the modem and or power cycling it can clear out the mac address it remembers so it can be replaced with the mac address of the router to authenticate and be assigned a wan ip address. If you have no tried these steps yet please do.
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HBMIAuthor Commented:
Couple other notes:  The lights on the router do light up (internet, ports, power)  I plug my router back in and everthing works fine.
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hallcomisCommented:
Try cloning the MAC from the cable modem.  I had the exact same issue with my cable provider (Charter) and as soon as i cloned the MAC and rebooted the modem and router after applying the changes I was in  business.
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Marius GunnerudSenior Systems EngineerCommented:
A few things to check out:
1. make sure the IP address of the wireless router is not the same as the cable modem's
2. where is DHCP being issued from ( cable modem or wireless router?) make sure only one and not both are issuing DHCP.
3. If cable modem is issuing DHCP make sure wireless router is correctly configured as an access point.
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