how to make an usb works with a mac ?

I'm assuming you are referring to a flash drive.

You didn't say whether you used to use this on a Mac or Windows computer...might be helpful for us to know.

At any rate, you'll probably want to reformat the flash drive. Here's how to do this using the Disk Utility app on your MacBook Air. (Disk Utility can be found by going to the Finder-->Applications-->Utilities): Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Hope this helps.

nadir215 Said:

"how to make an usb works with a mac ?: I can't open an usb card that I used to use."

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What do your mean "usb card"

Are you asking abut a flash drive? Or a hub? Or something else?

Disable USB Device:

Perhaps the device is intermittently disabled? See here: If you See USB Devices Disabled on your Mac - Apple Support