Thanks for posting in the forums. I'm sorry to hear you are unable to get a video signal when using the component input on your Slingbox 500. It sounds like you may be experiencing a form of High Definition Copyright Protection called Selectable Output Control (SOC).
To test this, could you try disconnecting any HDMI connected to your cable box and testing the component input for a video signal? If this does not work, try rebooting your cable box after disconnecting HDMI. Some cable boxes don't unblock the input until the cable box is rebooted.
If this does work, you will need an additional set of component cables going OUT of your Slingbox to your TV in order to get a video signal on your television.
Below is a link to an article that explains in more detail what is possible happening:
Hope this helps!
The Sling Moderation Team