Lot's of people. Do a Forum Search on 'no manufactures' and you will see them. Basically U21, a TS1117 3.3V voltage regulator, has failed. Contrary to what you were told the Support people know all about this as it is a know design fault, and lots of people seem to have got their Slingboxes replaced even outside warranty.
Thanks for using our Answers forum. I understand that you cannot enter your cable box in the setup screen. This article, Help finding your video source with the supported video sources widget should help you find your source. The other thing you can try, is just entering your cable provider.
Hope this information helps.
Sling Moderation Team.