As dc3 stated, Desktop Doctor is NOT vital. You can safely uninstall it.
I do want to know if, when setting up your Comcast internet service, did the Comcast toolbar get installed on your computer? If it did, UNINSTALL it. It's flaky, and has been known to cause issues which disappear once the toolbar is uninstalled.
For future reference, you do NOT have to install anything from a disk when setting up your Comcast modem. All you have to do is make all your connections, and call Comcast to have them provision the modem.
I also want to direct you to the Comcast help forums. Those forums are provided to Comcast customers, and are a great resource for vendor specific issues. There are forums for computer issues, email issues, security, internet, cable tv, and CDV. Many times we, the users there, can provide answers tech support and customer service can't.
Click the link below, you'll be sent to the sign in page. Log in with your Comcast user ID (the part before .net) and your password. You will next see a first time forum users page, asking you to choose a screen name for use in the forums. Once you set that up, you'll be taken to the actual forums. http://forums.comcast.net/comcastsupport/
(Once you get to the forum, save the page to your favorites. If you want to get to it from the Comcast home page, you have to jump through hoops to reach it)