Hi Seanarice, welcome to the Seven Forums.
First, I recommend you reconnect your router. It's always better to connect through a router and a modem, than only a modem. A router is much more than just a device to split your connection to multiple computers, wired or wireless. This
article tells you more, if you are interested in finding out more.
If you really insist of using only the modem, you have to set it up. When you still had your router connected, the information needed for you to be able to connect to your ISP Comcast and further to the Internet was stored in the router. Disconnecting it leaves the modem with no valid information on how and where to connect. The lights are on or blinking to show it's ready; it understands it's connected to the net, and to your computer, but does not know how to use this information.
Not knowing the make and model of your modem, call Comcast again and ask how to set up your connection. You have most probably received a setup CD with the modem, you could also start by running it on your computer and following instructions given on screen.
Hope this helps at least a bit. Come back if you have any more questions.