Sounds like it MIGHT be a failure of the power supply for the SB Pro-HD -- hopefully, not something worse inside the SB. If you are still under warranty I believe you can get a free replacement power supply from Sling Media. And if it is still under warranty, perhaps they will instead replace the entire unit?
If no longer under warranty, you might first try replacing the power supply, then do a hard reset of the SB and try to do the reinstallation procedure.
These are just my guesses based on reading reports from others with similar symptoms on this forum. I have never experienced such problems myself (knock on wood). However, I did notice early on that my SB would get physically quite hot to the touch, so I removed it from my media cabinet and placed it on the floor behind with extensions to its "feet", so that there is more air circulation around the box. Seems to run a bit cooler now.