This happened to me last night. All of a sudden I lost internet connection. After checking everything possible on my laptop, I moved onto checking up on my router. And after checking everything on my dd-wrt, I ran out of things to check. Then I realized maybe comcast was down. I then quickly grabbed my phone (thanks to 4G) and checked, sure enough it was comcast. Here is the page to check for your comcast status. You will need to login using your comcast user/pass.
http://customer.comcast.com/help-and-support/
Click on Sign in in the Your Dashboard widget on the right to get started. Then you will see something like this.
Good to know they are already working on the problem.