Router = good / Modem = BAD :( HELP!

I have:

Linksys cable modem BEFCMU10
& Linksys router BEFSR41
Computer is an AMD with a ASUS A7V with on board network, device manager says it’s a SIS 900 based PCI Ethernet Adapter.

OK Here is the problem. I can surf the internet fine when the compute is plugged into the router. But if I try to use it plugged straight into the cable modem it will not work! It’s my Ex-Wifs's (was mine but I gave it to her) computer and she dose not have a router. I can’t for the life of me figure why the hell the internet works through a router but not when plugged straight into the god damn cable modem! She even had the COX cable guy there for 2 hours and he couldn't fix the problem (not surprisingly).

Also note, it was working for a good month plugged straight into her cable modem but then it just stopped one day. The computer had a TON of spyware so I reformatted thinking that was the problem and put a clean copy of XP on it. It was working good at my house (through a router) until I tried to make it work using just the modem.

Ok so what do I do?

It this an easy fix? Or should I just buy a god damn router and stop dicking with it?

thats odd. I would try a different cable as it may have been damaged but the switch of the router compensates for it. Really I am a little stumped.

I can definitely rule out the cable. I have tried 3 different cables and all had the same results.

I think I can also rule out the cable modem because the computer refuses to work plugged into two different cable modems. It’s just crazy how when I plug it into the route it works fine!

I said screw it and spent $49.99 on a linksys router and guess what? It works, problem solved. I would really like to know what caused it for the future but o well, at least it’s fixed…

Some cable modems like to hang onto MAC addresses allocations and wont let go. This was probably because the modem was expecting 1 mac address and got another. Its very common, for some reason.

To fix it, you either have to unplug it for a long time, or reset the modem's settings.