Did your friend set up both computers for the router?? Am assuming Red hat for you, does he/she also use Linux? Which distro, if so. Can your friend's computer get out on the net? Are you using the command line or a GUI on your Linux box? Ethernet or Wireless?? How many ports on the router? >SSN, birthdate, address, and major credit card?< heh
Things to check...
Check if any lights show up on the nic. See if the Router light shows for your connection. Mind you, there should be atleast 2 lan lights showing, unless your friend has shutdown his/her computer.
No lights on either end of your connection?
I would first, check the connection, if connected by ethernet cable, at the router and your nic card to make sure it is secure. Check for severe pinches(like "V" shaped or worse) in the ethernet cable as well(if you are able). Are you using new ethernet cable, if so, is the cable cat5 or another category, suitable for your network? Hopefully there are no length issues; if so you may need a repeater to push the signal to your system. The longest I've used is 25' w/o one, I don't know beyond.
If all checks, I would setup the modem again to see if it will run on your machine minus the router, basically as you had it set up. If it works, I feel either the router may not be correctly setup to see both computers or your computer is not setup correctly for the router.
Lights on one end, but not the other end of your connection.
Kink in the cable or broken, other networking equipment necessary to carry the signal, port blown on the router or PCI/ISA slot blown on the motherboard, and I'm sure other problems that I am missing...
Lights on both ends of your connection -- regardless of color?
Configuration problem. Don't know how incompatible hardware acts on Linux boxes though.
Quite honestly, if the modem worked before with your computer, and the router was setup correctly, the problem sounds like a loose connection on your nic's end OR the router end(this could also include the length issue or kinks, I mentioned). I am, of course, assuming you are using the ethernet rather than wireless.