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An all-white screen means some sort of memory failure, perhaps. Or a failure of brightness limitation / too-strong-contrast, or the like.
Overheating means a short, and/or an overvoltage.
A humming sound is an oscillation, owing to some instability in the circuitry. Or, if it happens when plugged into an AC adapter/charger, it could mean the charger is defective and is introducing AC into the phone.
If I were repairing it, I would check for poor regulation of voltage from the battery, and/or (owing to some overcharging error) excessive voltage from the battery itself(?)