With a big regulated lab power supply, I reconnected my Slingbox Classic to the system. The network light comes on when the box power is applied and when I start the Slingbox software, my PC says I'm connected and the upside down U lights. When I stop the Sling Media software, the upside down U light goes off. I can change channels on my cable box. The display on my PC is normal but I get a message telling me that the audio/video is either weak or non-existant.
The message you got is about the TV source attached to your Slingbox. It indicates that the TV source is not on. You need to press the Power On button on the virtual remote control. Regarding the first post, the issue seems to be related to the Power Adapter.
The following link will allow you to know how to purchase the Power Adapter.