Thanks for using our answers forum here! I'm sorry to hear that you are having this issue with your Slingbox 350. Are you using the external IR Emitter? Have you checked the cable box remote control settings? In order for the Slingbox to communicate with the cable box, the remote settings will need to be set to IR (Infrared) and not RF (Radio Frequency).
Here is an article from our support site with some additional troubleshooting steps that you can try:
Hope this helps!
The Sling Moderation Team