I did what I believe is a factory reset. I held the button down until the network light flashes twice quickly and released it. The unit powers up and the remote doesn't work and it can't be seen on the network by the slingbox setup software.The screen shown is the getting started screen on the TV but the unit is unresponsive from the remote or the network.
I can ping the device and get a response in this mode but the sling setup says that it could not find any slingboxes on my network.
The weird thing is that if I just do the quick reset, the box is seen by the software, still has the latest firmware (didn't get reset to an older version during the factory reset which I was hoping for..) but it says it isn't saved and needs to be reset.
What you may want to try is reset the Slingbox 500 by pressing and holding the reset button down for 1 minute. Once you have reset the Slingbox you can move it to the main router and wire it with an Ethernet cable. You should then be able to complete the setup on a laptop or desktop computer and get the Slingbox associated with the account.
As for deleting the Slingbox 350 that seems to be on your account there is a way to do that. What you will want to do is hover over the Slingbox 350 that is listed in the directory there will be an option to delete the Slingbox on the right hand side.
Here are articles that may help with the remote functions as well as deleting an unwanted Slingbox from the directory:
Hope this helps!
The Sling Moderation Team - Leanne