Unable to sign on to MacBook Air

I‘m unable to sign on to my MacBook Air. I do hear the start up sound, but then the screen goes black. The apple logo appears and looks like it’s downloading something. Then 2 graphics appear. On looks like a vertical eclipse with 2 vertical lines inside of it. There is a small arrow pointing up. The second graphic looks as if you are looking at the side of a laptop. It is a narrow horizontal rectangle with a small arrow pointing to the left. The graphics alternate back and forth. I’ve called Apple support without any success. Tried rebooting, shutting down, but nothing happens. I am unable to use keyboard or the keypad. Any ideas?