Sony DSC-P20 Operating Instructions (primary manual) Operating Instructions Manual page 75

Symptom
No function works though
the power is on.
Cause and/or Solution
t Remove the battery pack, then install it again
after about one minute. If the function still do
not work, press the reset button located on the
bottom using a sharp-pointed object. (If you
press the reset button, the date and time setting
is cleared.)
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