Macbook air suddenly shut down and now will not turn on. What happened and how do i fix it

Can you tell us which MacBook Air do you have? It's the one with MagSafe 2 power adapter or usb-c power adapter?

MacBook Air pre-2018 (MagSafe 2) are known to have this kind of problems. You need to take the computer to Apple or an AASP to run some tests (Power On Pads being one of them) and so verify wich is the faulty part. Based on my experience, the Main Logic Board is the responsable for those non-turning on events.

OK, it's a T2 MBA.

Green LED on the Caps Lock key turns on?

Since you already claimed that you tried resetting PRAM/SMC and nothing happened the last test would be to borrow another T2 MacBook and download Apple Configurator 2 from the App Store. Once installed you should read this article and try to revive/restore the computer -> https://support.apple.com/guide/apple-configurator-2/revive-or-restore-an-intel-based-mac-apdebea5be51/mac

The support article you came here from provides you with the basic troubleshooting steps to take in this situation. Have you tried them all yet? If so, where did they fail?

Here are some articles that may help.

• If your Mac doesn't turn on - Apple Support
• If your Mac doesn't start up all the way - Apple Support
• If your Mac restarted because of a problem - Apple Support