Why is there no program when the program is written into the PLC and then powered on again?

plc contains two storage areas, RAM area and FLASH area.
There are two situations where there is no program after power on again:
1. After writing the program to the RAM area, it is not written to the FLASH area.
Rewrite the program, enter the online mode test, stop the PLC, and write the PLC program into FLASH. After the prompt is written, turn the DIP switch of the PLC to RUN (running gear).
2. The program has been written to FLASH, and the DIP switch of the PLC is not set to the RUN position to power on.
Turn the DIP switch of the PLC to RUN (running gear), then turn off the power, and wait for a few seconds to turn on the power.