The email on my MacBook Air is flashing

This morning the email on my MacBook Air was flashing. I followed the guidance given in the last entry on this topic. I couldn’t find a button to force quit and so got as far only as quitting the apps. Now my screen is stuck on the background image. The computer won’t shut down or reopen. It is ten years old at least. Has it died? Grateful for any advice.

[Re-Titled by Moderator]