Netgear ProSafe FVS318N router

I'm trying to install Netgear ProSafe FVS318N router and having lots of problems. When I attempt to log in to the router's web interface, I get a warning in Internet Explorer that the “security certificate is not valid” or it says “Your connection is not private” in Chrome. Is that normal? I can agree to proceed to the router’s web interface webpage and log into the router. However, sometimes I can’t access the router’s webpage at all and get a “web page can not be displayed” even though I can still ping the router. I have to power cycle the router before I can log back into it. The biggest problem is the router will not get online and stay online. It will sometimes get online for a few seconds but then it's as if the connection is blocked and it won’t get online. I can ping the router and I’ve verified that it has an IP address from the ISP. I can get online with another router just fine and a PC connected directly the cable modem gets online just fine. I’ve spoken with the ISP and they tell me they can see that the Netgear is connected and they say everything looks good as far as they can tell but none of the PCs connected to the router with wired and wireless connections can get online. I also have a occasional problem connecting to the router wirelessly. I frequently get “Can not connect to this network”. But other times I can connect to the router wirelessly just fine. I would think this router is faulty but I took it to another location and it worked fine! I’ve listed the steps I’ve done to correct this problem below.
1. Reset the router to it’s default settings.
2. Updated the firmware to the latest version
3. Reset the router to it’s default settings.
4. Replaced the cable modem
5. Disconnected all Ethernet cables except for the cable modem.
6. Change DNS settings in the router and in the PC’s network connection to OpenDNS.
None of these steps worked. I’m about to return this router and get a different brand. PLEASE HELP.