Q: My MacBook air wouldn't turn and all I get is a black screen with a circle crossed out that blinks every once and awhile

My Macbook air wouldn't turn on and all I ger is a black screen with circle that is crossed out that blinks every once and a while.  The last thinI I did was the thing that encrypts your data.  I tried to press back on that but that isn't work so i just turned it off by pressing on the power button for a few seconds.  What should I do to fix this?