I don't know what I clicked on, but I cannot play or stop or edit my video. Plus, nothing appears on the screen. It's black even though a footage is on the timeline. See screenshot. Where is the play button? And the stop ??
Depending on the state of the program, ie a project has been saved with the controls 'missing' the F9 may not work it returns you to a previous saved 'state'.
If so, select the Standard option in the image @me_again posted above.