Always start by unplugging the box and give it a few minutes, plug it back in, and give it an hour or so for all the apps to reload. Then try it.
Doubtful, but check the interactive menu to make sure it is still turned on.
With your Comcast remote do the following:
press "menu"
press "menu"
select "interactive tv"
select "caller id"
check that it is still turned on
If none of that helps, then please call into Comcast support as they will need to check that your set top box is properly tied to your CDV phone account.
