If you had also said the horseshoe LED was permanently on I would have said you had the classic symptoms of a failed power adapter (After telling you off for not searching the forum before posting, as this is a common problem )
Even if it isn't, that should be your first step. And don't just buy a third-party one, the Pro-HD is VERY sensitive to power supplies, so get one from Sling.
My Sling HD recently stopped working. I noticed it first when the TV that I pass the component video through the Sling with lost its sound. Now I can't get the sling to show up on the local network or remotely. I am only getting a power light. I have tried the reset button but it does not reset. Switched the network cable just in case. Nothing will get it to react or reset.
Any ideas or did this one bite the dust?