Cable Modem: Router vs Straight Connection

I am experiencing the weirdest problem.
When I originally subscribed to Cable Modem Service I had only one computer and the Cat5 cord was plugged directly into the Cable Modem.
I heard about all the nasty haxorz breaking into peoples computers and that a router would block most attempts to break into my computer.
I bought a Netgear RT 314 Internet Gateway Router and it worked fine from day one.
A year ago at Christmas time I needed Ports available so I would temporarily take the Router out of the loop and connect the Main Computer directly to the Cable Modem and it worked fine.
The Cable ISP has since changed a lot of things and now I go to bypass the NetGear Router and Connect Directly to the Cable Modem and I am Unable to do so. I know that the Computers TCP/IP settings are correct (auto-detect IP address) and I have even tried with different Cat5 cables and my laptop and Cannot Figure out why I am unable to Directly Connect a Computer to the Cable Modem. I have turned the Modem off Numerous Times for more than a minute and let it reset to no avail.
Can Anyone Explain How/Why this is Happening???

Your cable ISP might be tracking/registering the MAC address of network cards on their network. Some ISP's do this to prevent unauthorized use of their network. If your ISP has started doing this, since your router and your computer's network card have different MAC addresses, your ISP wouldn't allow your computer to connect directly.

What you can do instead of taking your router physically out of the loop is go into your router's configuration and put your computer's local IP address into the DMZ. This way, incoming packets to your router's WAN address are automatically routed to your computer on the LAN. Or you could specifically forward the ports for the app you need to your computer's LAN IP address.

Ok, With that Idea in Mind I went back through the customer support pages and see that they set a limit of 3 computers hooked to a home network and if you add a computer you have to go through some automated process involving your account password etc. I guess thats to unlock the modem so it can detect another authorized MAC address.
I wish there was an easy way to get the MAC address off the NetGear RT 314 router and then have my computer spoof it. Anyway, I at last know what the problem is now....thanks