I understand that you have video issues with the Slingbox Classic. Unfortunately, your post is not clear enough since you didn't mention what type of cables are you using to connect the Slingbox to the TV source (cable box, satellite receiver, DVR). I recommend resetting the Slingbox to factory settings and then run the Setup Assistant. If you have the same issue during the setup, I recommend you to try a different set of cables and also a different source, like a DVD, to determine if the issue persists.
Regards and hope this helps.