Networking iMac and MacBook Pro

Well, doesn't work on iMac. I can't enable File Sharing, clicked on the box to left of File Sharing, but nothing happens. The help text confirms that file sharing is off.

On Mac Book Pro, don't have that problem. I can select/de-select file sharing.

So, what could cause problem with Mac?

Well, there is no padlock at the bottom. Attached, is screen capture. Padlocks are required in other areas, such as Users & Groups, Security & Privacy, but not in Sharing.

Any other thoughts? Thanks, Vince

Thanks, Vince

That worked! Yea! Thanks!

But now new related problem

My iMac now shows up in Finder on the MacBook, but when I select it, I click on the Connect As... box. I'm the registered user for both devices, administrator, and use same user names on both. Yet when I enter the user name "Vincent Black" and the known password, it's not recognized. That same user name is in the Sharing section on the iMac, shared folders, Users listing, with read & write privileges.

So what am I doing wrong now?

Screen sharing, printer sharing, remote management, remote apple events, content sharing and bluetooth sharing all allow check marks.

File, Media and internet sharing, do not.