It seems that you are having some issues with your Slingbox PRO-HD since all of a sudden it has lost the video signal.
I recommend you to contact your parents and ask them about the cables connected from the Slingbox to the set top box. Since you did not mention any information about any possible error message, I also recommend you to check if you are using an HDMI cable to connect the set top box to your TV set.
If this is the case, you will need to remove the HDMI cable since it is not compatible with the Slingbox due to the HDCP restrictions. The only workaround for this possible scenario is to use the Component cable (RGB) from the set top box to your TV set and to the Slingbox. Further details are included on this link:
If the virtual remote control does not respond, I encourage you to run the AV source configuration one more time and make sure to place the IR Blasters right in front of the set top box IR sensors. Feel free to check this link in order to get detailed instructions:
Hope this helps.