Tool bar recording volume slider locked

I get a notice "recording volume ( unavailable: use systems mixer) it was working previously. Have I clicked on something inadvertently? How to fix?

Have you changed the recording device?
Some devices (notably USB devices) don’t have software level control.

I have been recording from a tape player connected directly to my Mac. I am new to audacity so I don’t know where to go. It worked initially, using the aforementioned connection and also using my blue yeti microphone. I hate to have to download Audacity again. Is there a step by step procedure that I can go through to eliminate any erroneous settings?

Don’t download Audacity again - that won’t help.
As Steve noted, you have probably set your recording device to a USB Audio CODEC. What is the selection for recording device in the Device Toolbar?
Have a look at this page.
– Bill