How to solve the error in a SIEMENS PLC

What is the reason for the error, there is no access to the CPU and also tried MRES but no result

There are two possibilities.

1.Flash memory card is corrupt for that you have to insert a new flash memory card or reinstall the program.

Also, remember do not insert or remove a flash card in power-up condition.

2.Bus fault also occurs check the I/o module especially analog I/O which have maximum connection load

3.please check the communication cable by inserting another plc or put a spare communication cable.

These steps need to follow step by step you get some idea of the problem

Switch OFF the CPU, remove the memory card, switch ON the CPU after 30 mins without a memory card.

Consider upgrading the firmware once the stop LED is stable.

Erase memory card, switch OFF the CPU, insert the memory card and switch it on.

Load the program

There is also another probability You have no backup battery so by turning off your PLC you erased your memory card. If you used the MRES switch, you also erased your memory card. The only thing to do now is to reload your program