Why screen showed this message. How to repair

You will need to reflash the ROM on this phone to see, most likely. You will need to download the ROM here and then use ODIN to flash the ROM back onto the phone.

If this does not work, the flash storage on the phone failed. You'll need to either replace the chips or the board; that said, I'd be hesitant to jump to this since a lot of older phones that aren't relatively new (read: best bet now is 5G phones from the last 3-5 years not from Sprint) are usually at risk of being on the next activation block chopping list for network shutdowns at elevated levels I would not buy them even used now. It's so bad at times now I even had to bump my tolerances to keep up with the risk to recent-ish 5G as the baseline. It may be time for a new (factory unlocked) phone if the NAND flash is dead with how risky some of these old 4G phones are getting in the future.

At this point, I'm telling people with these old "at risk" phones to rock them until they die if you’re not in a rush sure but I wouldn’t spend money on them if things like batteries wore down.