Solved: how to hard reset Psion Series 5MX: press the unfolded paperclip into the reset hole as for the soft reset. Then, hold down...

How do I reset the Series 5?

If you find that you cannot exit a program normally, move to the
System screen and select the List open files command from the
File menu. Select the program from the list and press the Close
file button.
If this does not work, or if your Series 5 appears to have “locked
up”, you can always perform a “soft reset”. This should restart
your Series 5 while preserving most of your information.
It is worth trying a soft reset if the keys on the Series 5 do not
appear to respond, or if the Series 5 does appear to switch on
and you are sure the batteries are good (especially if the contrast
adjustment still appears to work), but the screen is otherwise
blank.
· To perform a soft reset: gently press something like an
unfolded paperclip into the reset hole, above the backup
battery location.
After a soft reset, any changes to open Word or Sheet files (or
OPL programs) will be lost. Your other files on the Internal disk
will almost always be safe.
It is possible (although unlikely) that a program failure causes the
reset to lose the information on the Internal disk; it could even
prevent the reset from working at all. If this happens, you will
have to perform a “hard reset”.
· To perform a hard reset: press the unfolded paperclip
into the reset hole as for the soft reset. Then, hold down
both Shift keys, and press Esc to switch on.
Important: A hard reset resets the Series 5 completely, and all
information on the Internal disk will be lost.

Psion Series 5MX hard reset