Damage to screen or posible crash in the system. one you shouldn't hear anything when you wake your psp from sleep, everything is solid state inside so no moving parts except the UMD disk reader.
Try shutting down the psp by holding the power button up for more that 10 seconds. then turn it back on. if it doesn't work then take it in.
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Writting something down is giving my mind permisson to forget it.