You probably need to reset the Slingbox back to factory defaults. If your Player's directory can't find a Slingbox attached to the same network-- and there's nothing wrong with the hardware-- there's something funky going on with the IP address it's parked on. Doing a hard reset usually fixes that. You'll also need to run the setup assistant again.
Here's a support doc that covers this:
Here's the same info with a fancy video tutorial:
Hope this helps,