Okay so if that happens it either means the EEPROM on the Sense HAT isn't working, or the EEPROM ID pins are not connected between the HAT and the Pi. Which happens if you're using a shorter pin header.
The good news is you can override this by adding a line to config.txt
. Open a Terminal window and enter the command below:
Scroll to the bottom of the file and append this line:
Now press Ctrl - O, followed by Enter to Save. Then Ctrl - X to quit.
Then type in the command below to reboot:
Hopefully that should do it. If this doesn't help it might be that you need to update your SD card to the latest version and then try again.