An alarm went off on my MacBook Air.

It seems to be diagnostic beeps at the beginning... indeed, if you give us the number of beeps and their length, for example, 2 long beeps and 1 short beep, we might be able to tell you what the issue is...

Hello,

an alarm? What do you mean?

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Windows has not detected any keyboard. Press Enter to continue.
Huh?

It's like an alert, it keeps ringing non-stop for an hour now :( And my Mac isn't working anymore ??? Thanks again

Hello

 An alarm went off on my MacBook Air non-stop, what should I do?? Thank youuuuu 

It depends, several solutions are available to you,
for example:

-call the fire department
-call Emergency Police
-call the caretaker
-turn off the oven
-check if the freezer is not open
-get up to go to work
-turn off the washing machine
-drive the kids to school
-go to the hairdresser
-replace the anti-scale cartridge
-delete the programmed alarm if it has become unnecessary

etc... etc...

in short, you got it, without essential details we don’t know what the best advice is...

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Have a great day, or a very good night... :)
Francis.