Unattended Service Account

I'm attempting to set up the Unattended Services Account for Power Pivot via Sharepoint. My boss set up this server, and I really don't know how he did it. (if he followed the wizards or what...) When I go into Central Admin-->Manage Service Applications and open the Default PowerPivot Service Application, I see the name of the Unattended Service Account. However, when I go into the Secure Service area and find that name, it doesn't appear to be set up. When I'm on the screen that should show me which Windows login and password are being used, they're empty and it says "Credential fields cannot be added or removed at this time. Only the 'Masked' property can be updated." Where can I go to set this up? I know something is wrong because if I try to go to Central Admin-->Manage Service Applications and then click on the Default PowerPivot Service Application, it tries to open the server health dashboard, but I get a pop up "An error has occurred." Not very informational.

Excel Services seems to be working ok. Power Pivot uses Excel Services to render, doesn't it? Why are there 2 separate services?