I've tried everything - fatal error: HID.h: No such file or directory

I'm not familiar with the Digispark.

Does the file HID.h exist at the given location? Note that includes might be case sensitive on Windows systems, not sure; so if you do find e.g Hid.h, it might be the cause.

Note to others: the Digispark possibly has a software USB emulation. Please note that OP said that it worked before.