I can understand why you have contacted us in regards to the poor picture quality. Below are some suggestions to help resolve the issue you're experiencing.
-If your computer is connected via Wi-Fi, you can try connecting with an ethernet cable.
-If all the channels are showing "grainy", it could be a connection issue with the coaxial cable. Make sure both ends of the connection are tightly secure. As well as, swapping out the coaxial cable and trying a different cable.
-Also if you have changed the streaming quality setting, it's recommended to remain on "Auto"
We hope this helps.
The Sling Moderation Team
That coax connector between wall and SB can indeed be very sensitive to tightness. I was getting grainy images on my TV (before putting the SB in the loop), and the TV service provider technician walked me through the tightening process over the telephone. Tightening that connector on the back of the TV by less than 1/16th of a turn made all the difference in the world -- completely eliminating the graininess. You might give it a try, or, as suggested, try replacing the coax cable with another -- which might have developed internal problems in the process of putting the SB into the connection loop.