It seems that you are having some issues with your Slingbox PRO-HD since you cannot longer use the DVR features.
Just to clarify, the Slingbox does not have recording capabilities. Once we have clarified this situation, I recommend you to run the A/V source one more time in order to verify if you can control the DVR attached to your Slingbox PRO-HD. It does not matter if you are away from your Slingbox. You only need to know your Slingbox administrator password in order to run this process. Just go to www.setup.slingbox.com and follow the steps for the TV source configuration.
Hope this helps.