It's possible it could be the power supply. If you try a replacement just make sure it matches the exact wattage/specs as the original.
I'd also try a factory reset (not sure if you did a soft or hard reset previously) Slingbox.com - How to reset your Slingbox to factory settings
Here's a link to the accessory page if you want to buy one directly: http://www.slingbox.com/Buy/Accessories.aspx
I also have the PRO-HD and love it, but you may want to look at the M1, as it benefits from a WiFi setup (less cables) and has full HD streaming.
Thank you for the reply. I am trying a new power supply and that seems to have done the trick. I still may get another new SlingBox, though. I have been eying up the Channel Master DVR +. It looks like the only SlingBox that it is compatible with is the Slingbox 500/SlingTV. I will start watching for sale prices on that and the Channel Master DVR+!
This morning I tried to connect to my Slingbox PRO HD via my Android Nexus 7 tablet. It displays the message "Invalid password Incorrect Slingbox password. Please enter the correct password to connect." When I try to connect via a personal computer running Windows 7, there is no longer a Slingbox shown in the Directory. I reset the PRO HD, but it didn't seem to change anything. I have read that the power adapter can be a culprit. I am still getting lights displayed. Could the power supply still be a culprit? Do they sometimes simply not provide enough power?
Also, if I decide to place it, should I consider a new old stock from Amazon for $99.99 or should I look at a newer one? Are the newer ones more reliable? I have seen the Slingbox M1 at my local Wal-Mart for $149.99. I have also seen the Slingbox 350 on sale at Best Buy for $99.99. The Slingbox 500/Sling TV is $249.99.