Are you sure your WiFi connection is bridged to the same network as your Slingbox?
As a test, I recommend getting the IP address of your Slingbox. While "hardwired" into your network, bring up the Slingbox Application on the command bar, select Help | About Slingbox <model> (Alt +E) | Information Tab. There in the Lan subsection, you'll find the IP address assigned to your Slingbox. Write that number down, then open a command prompt (Start | Accessories | Command Prompt). Now "ping <Slingbox IP address>" You should see information information about the connectivity. Now, disconnect the hard wire and setup the laptio for WiFi access. Go back to the Command Prompt and perform the same ping test and see if you get the same results or different.