Check the following points to resolve the issue:

Your machine cannot detect the toner cartridge for the color indicated on the machine's display.

Remove the toner cartridge for the color indicated on the machine's display from the drum unit, and put the toner cartridge back into the drum unit.

Your machine cannot detect the belt unit.

Remove the belt unit from your machine, and put the belt unit back into the machine.

Your machine cannot detect the drum unit.

Remove the drum unit from your machine, and put the drum unit back into the machine.