Problem with Dual Cable Connections

Hey guys, I haven't been on the forums in awhile, but its good to be back.

Well, I return with nothing but problems and was hoping to get some help. Here is the scenario:

I have two separate 3mb cable connections. Each have their own dynamic IP address and are setup as two completely different LANs. I setup this connection for a roomy (who by the way is a bandwidth hog ) and also to do in house security tests from one connection to another.
I have recently removed my second cable connection and since then my internet keeps dropping. I have tried running the cable modem alone without the router, connection drops. I bought another modem and tried with that one, connection drops. I tried the modem from my second connection, and yes you guessed it, connection drops. The fix right now is simply power cycling the modem.
I have contacted my ISP numerous times. They run tests and say everything looks good on there end. They blame it on the router or tell me the modem is bad. But that is 3 modems, I hightly doubt there all bad.
I also had them update my DOCSIS firmware and re-register my modem MAC Address in there system.
An odd thing I noticed was, when I leave the 2nd modem powered, but no network cables plugged in, the cable LED stays lit when the 1st modem drops its connection. But other times both LEDs will go out when the connection drops. (Keeping in mind the 2nd modem connetion was cancelled from the ISP.) Sorry about the explanation, its one of those where explaining it in person or just seeing for yourself is easier.
Does anybody have any ideas to what is causing this problem or another troubleshooting idea that I might have missed.

Thanks for the help guys. Talk to you soon.

ZiPPy

No ideas huh???

No, unless your ISP did something silly when they ceased your other connection. I dunno...

There's a good chance your connection keeps resetting itself because it is being flooded. This happened to my DSL line constantly before I put a cap on my bittorrent upstream. Check your total throughput; if either your upstream or downstream traffic is nearing the line's maximum, you may want to consider putting caps on bandwidth-intensive applications.