We need to get more information about the connections with the Slingbox, you need to be as specific as possible. What type of cables are you using to connect the Slingbox with the TV source (Cable box, Satellite, DVD, DVR or coaxial). Have you tried a different type of cables or another source? Do you have the same issue if you connect to the Slingbox using a different PC/Mac?
If the issue persists after testing different cables, source and the computer; I recommend to Restore your Slingbox to Factory Settings