It seems that you are having some issues with the Slingbox video signal since you get the "weak or no video signal detected" error message.
The main issue in this case is that you are using the HDMI cable connected to your DVR. As a matter of fact, none of the available Slingbox models will work if you use the HDMI cable, due to the HDCP restrictions. The following links will provide you with the explanation and a possible workaround for this issue:
Hope this helps!