The password that is being asked for, sounds like your admin password rather than your base account password. This would have been created when you first set up the Slingbox and may not have been used since. I'll link some troubleshooting steps below, just in case.
- Slingbox.com - SlingPlayer repeatedly asks for the Administrator password
- Slingbox.com - How to reset your Slingbox
If the steps in the first article do not work, you will need to process a full factory reset.
I hope this helps!!
Sling Media Technical Support