I have happened across this problem when uninstalling Comodo Internet Security where the uninstall freezes and you have to use task manager to end processes or restart and afterward there is no internet connectivity I have had this happen personally and have read of this issues on other related forums.
What causes this is the firewall driver for Comodo fails to uninstall and the fix:
On XP open network connections and right click on your network adapter and go to properties
On Vista go to Network and Sharing Center Manage network connections and right click on network adapter
Once you are in the properties for the network adapter look for entries for Comodo firewall driver i believe it leaves two entries these fail to uninstall and cause the lose of internet connectivity highlight those and choose uninstall once that's done click ok and close out of all open screens and try your browser if it is still not working restart your computer and afterward you should have restored internet connectivity hope this helps!
