PL 390 seems to have frozen


Help needed. Today my PL 390 seems to have frozen. Display screen shows:
time(still,not blinking),
battery status(approximately 60%)
and lock icon.
It won't unlock,despite several trials.The cells were taken out and replaced with freshly charged 3AA 's,but to no avail.
Connected it to laptop USB,with charging cable,still same status.
It was workingly perfectly yesterday.
Any suggestions are welcome.

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