Well the 6190 isn't the best modem and is known for some problems:
http://www.badmodems.com
I would recommend getting into a Broadcom based modem if your ISP supports other model modems.
Who is your ISP?
Have you swapped LAN cables between the modem and router?
I recommend that you have your ISP check the cabling going to the ISP modem, check signal levels going to the ISP modem. For cable Internet, RG-6 coaxial cable is needed, not RG-59. Check for t.v. line splitters and remove them as they can introduce noise on the line and lower the signal going to the ISP modem. Connecting to the ISP modem could result in a false positive as the signal to the modem could be just enough to that point then adding on a router, could see problems. Ensure modem is working well too. Bad modems are out there as well. The router operation is dependent upon getting good data flow from the ISP modem and the modem is dependent upon getting good signal from the ISP Service.
