If your HP scanner not working then below are some of the reasons for the scanning failures with HP printers:-
1. If you have updated your OS recently then the printer driver might not be compatible with the latest version of the OS.
2. Your HP printer might be disconnected from Wifi.
3. The USB or ethernet cable might not be plugged properly to the printer.
4. The scanner unit of the printer might be turned off.
5. There might be an issue with the paper jam.