There are several ways to reset a Comcast cable box. Sometimes, issues with a Comcast cable box, such as not processing a proper cable signal, can be resolved by turning the box off and on again. Also, check that the cable connections are secure and the power outlet is working.
If the cable box cannot be reset at home, one can call Comcast support at 1-800-COMCAST and ask a technical support representative to send a reset signal to the box. After the customer support representative sends a reset signal, he can analyze the problem. It can take several minutes for the reset signal to take effect.
In case phone support is not available at the time, Comcast also offers downloadable user manuals for various cable boxes as online references; the instructions vary depending on the type of cable box.