I'll be more than happy to help! There are two possibilities as to why you are not getting any video. As long as your cable box does not have an HDMI connected to it, then it is not an SOC issue. That leaves only one possibility, and most likely is the resolution your set top box is set to. Try switching to a supported resolution, even though it may have been working for you before. The links below will provide more information. Hope this helps!
- Slingbox.com - Troubleshooting "No Video Signal" errors during setup
- Slingbox.com - Video resolutions supported by Slingbox M1/M2, Slingbox 350, & Slingbox 500
Sling Media Moderation Team