Your 4500 can actually be any address you want it to be just as long as it's not the same IP address as your modems. I would do this first, do a reset of the router and let it get a connection to the Cable modem. It would auto connect with out changing anything. Once that's established, check ur PCs. They should connect and get to the internet fine. The routers default factory IP address is 192.168.0.1 with a subnet mask of 255.255.255.255 or 192. Once you can establish that the modem, router and PCs are connected and getting to the internet, then you have the choice of going back in can changing the routers IP address to something different. I would not change this if you do not have a lot of networking experience. I would leave it as is. If you do then fine, change the IP and subnet mask addresses to something of your choosing. I set mine to 6.#.##.1 for the routers IP address and 255.255.255.192 for the sub net. Also make sure that your Primary and 2ndary DNS server addresses are filled in on the Basic/Internet/Manual page. Sometimes they wont fill in. You can find this on the Status/Device Info/WAN section. Basically, keep things simple for your self. KISS! If it works then best to leave it unless you have the experience and knowledge to do more.
Once you get the setup going and everything connects, save off your config file so if you do go back in and make changes and good something up, you can reload ur saved file and it will set it back to the last known working state. Let us know how this goes.