What I understand from your post, is that you can't control your A/V source.
In this case, besides the troubleshoot that you performed, I would recommend to check the following links to discard the IR connection as a potential issue.
OK, in the end, bad IR cable right at the plug. Had spare Tivo IR cable but when I went to try it, wrong plug diameter for Slingbox!!!, Cut IR heads off Tivo cable and soldered to existing Slingbox cable. Still no go. Finally bought an adapter that fits Slingbox but allow me to use one of my other Tivo cables, and works great. So IR cable bad at plug. Slingbox uses smaller plug size than Tivo but cheap adapter allows Tivo IR cables to be plugged in and they work.