I'm a little late coming to this party, but I may have information that will solve this issue for some users.
The problem manifest itself in this way.
You use your Ender 3 for awhile without incident, then on power up, it seems to be brain dead. The screen backlight turns on, but nothing else happens.
Chances are, in some way your firmware has become corrupt. The solution is to load new firmware.
Now a caveat. My "solution" is based upon my first hand experience. My conclusions however, are based upon bits and pieces of information gleaned from dozens of sources and may not be accurate.-
First of all, this solution applies only to Creality machines which have a version 4.2.2 or higher controller board (the 32 bit boards) and does not apply to 8 bit boards.
Second, the problem occurs because of the manner in which these new boards handle firmware upgrades.
When the machine is powered up with an SD card inserted, the bootloader examines the SD card for the presence of ANY .bin file. When it finds one, it assumes that file is a firmware update which needs to be loaded.
Now this part is unconfirmed. Some sources say that the boot loader keeps track of the names of the .bin files which have previously been used to perform an update, and ignores the file on the SD card if that file has ever been used to perform an update. If the file is NOT in that list, the firmware performs no other tests, but assumes the file to be a valid firmware update. It loads the file into memory and turns control of the system over to the "new" firmware.
In my case, I had grabbed a spare SD card without checking the contents, loaded a gcode file onto the card, put it in the printer and powered up. It turned out that the card had a .bin file on it that was totally unrelated to my printer. The bootloader loaded that file and turned control over to this new firmware. Who knows what gyrations the new program put the controller through, but needless to say it was no longer the controller it was a few minutes ago.
Once I suspected what had happened, the solution was to find the correct .bin file, place it on an SD card, put the card into the machine and power up.
But here we again venture into suppositions which may not be facts.
First, if the bootloader has ever used a file with that name to update the firmware, it ignores the file. Since the file you use may come from the Creality web site, chances are it has the same name as the original firmware. The boot loaded will just ignore it. This appears to be the case for a number of you who after having tried to load the original "factory" software, see nothing changing. The solution for that is to rename the file to something so unique that the bootloader will not have used it before. Perhaps a name based upon todays date and time.
Second, the SD card used must be 8GB or less AND formatted as FAT32.
I'm assuming this has to do with the need to keep the bootloader small. Adding support for anything but the most basic file system would eat up needed bootloader program space. Since the memory available to non-bootloader code is MUCH larger than the space available for the bootloader code, additional file systems can be supported by the "main" firmware.
I hope this explanation helps someone in bringing their printer "back to life".
If any of my suppositions are incorrect, I invite all comments correcting my errors.