How to get my USB to work

It's possible that you had hardware failure or that the files on your USB key have been corrupted.

What you can do to test this out is plug the USB key into your PC. The Xbox 360 uses a PC-compatible format for the device, so it should show up and be detected there.

If your PC doesn't recognize the device, or it gives an error, or it wants to format the USB key, then you've probably got a hardware failure on the key itself. Unfortunately, recovering the files is going to be challenging. The Xbox 360 writes special files to the USB key, and if they are damaged in any way, chances are the data is unrecoverable.

If you can mount the device on your PC and you see an "Xbox360" folder with a bunch of "Data0000" files in it, then it is likely that the USB key is working properly. That would seem to indicate that there's an issue with your Xbox 360.

You can try a different USB port, or try turning it off and back on again, or check for updates to the Xbox 360 system software. You could also try using another USB key to see if that works. If none of these things work, it probably indicates a problem with your Xbox 360 that can't be fixed. You will want to contact Microsoft support and see what they can do for you.