Unfortunately I don't have much experience with Casio calculators. If it were Texas Instruments then I would recommend resetting it and if that didn't work, I'd blame it on a hardware issue and would recommend they use their warranty to get a new one.
Tiplanet.org or planet-casio.com are French communities but are much more knowledgeable about Casio and would be willing to help you in English.
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@tina93431 lets see if our resident calculator guru @thelastmill can help you out with this.
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