Soft Reboot (Hardware); Hard Reboot (With Memory Wipe) - HP 39g Master Manual

Just on the rare chance that you may find that the calculator locks up so
completely that the keyboard will not respond a method of reset is provided
which is independent of the keyboard. This should never happen but it is
important to know how to deal with it in case it happened during a test or an
exam.

Soft reboot (Hardware)

On the back of the calculator is a small hole. Poke a paper clip
or a pin into this hole and press gently on the switch inside. To
the calculator this is exactly equivalent to a soft reboot as
outlined on the previous page. If you do this when the calculator
is locked up then the chances are that you will find that the
procedure will not only unlock the calculator but retain your data
intact.

Hard reboot (with memory wipe)

To completely wipe the calculator's memory press
ON+SK1+SK6. Hold down the ON key and, while still holding it
down, press the first and then the last screen keys. Release
them in the opposite order. Don't release SK1 and SK6
together - release SK6, then SK1, then ON. This method will
always cause complete loss of data. If you find that the screen
fills with garbage, or if the calculator's in-built diagnostic routine
starts to run, then it is just that you have not released them in
the right order. Simply try again.
Calculator Tip
As a last resort, take the batteries out, including the disk
shaped back-up battery and wait a few hours. Reinsert the
batteries. Make SURE they go in correctly as you can very
seriously damage the calculator if you insert batteries the
wrong way around.
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