I will ad below the quick start guide for the Pro-HD. Anytime I have needed to do a factory reset on a older Slingbox model, I would always hold the button in for 45 seconds or more even. Also you would want to go to setup.slingbox.com to set up the Slingbox. I can add direct download links for the older desktop software, first one will be the download for Windows, and the second will be the direct download for a Mac, so make sure you click on one for your computer. The desktop software is another way to setup and watch your Slingbox,without using your Internet Browser. Make sure you are logged into your own Slingbox account to set up the Slingbox.
- Slingbox.com - How to reset your Slingbox
Hope this helps!!
Sling Media Support