I was playing Super Mario land 6 golden coins and collected 5 of the coins. I was in the middle of playing til the screen turned white so I turned it off. When I turned it back, my file was deleted? Why?!?!
closed as unclear what you're asking by Frank♦, Schism, Fabian Röling, Riley, Timmy Jim Jan 25 '18 at 12:44
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This is likely, and unfortunately, a dead battery.
In most older cartridge based games, the only way to keep save data was with a small battery connected inside each cartridge. It doesn't require much power to keep the save data, but 26 years is more than enough to drain them.
You can find several guides on how to replace these batteries (some brief research suggests that the original GB games might use the slightly smaller CR1616 battery rather than the CR2025 suggested for GBC games in the guides).
If you are not comfortable changing the battery yourself (it is a bit more involved than swapping out regular batteries), some stores may be able to do this for you for a price. Particularly stores that specialize in vintage video games.