https://www.flickr.com/groups/om-d_user/discuss/72157629730054480/

Some of these button presses may be extraneous - if you can shorten the sequences... good for you.

1. Power on with [menu] held down.
2. When LCD lights, release [menu].
3. [menu], [down] to spanner, [right], [down] to LCD brightness, [right] [info] [ok].

You're now at the banner which states the model name. From here you can go a number of ways -

4. [up] [down] [left] [right] [shutter] [up] for page 1 of status and then [right] or [down] or [left] for further status pages.

and/or

5. [up] [down] [left] [right] [shutter] [ok] for test parameter settings. Caution: I suspect that these settings could render your camera inoperable or unreliable.
and/or

6. Hold [menu]+[ok] together for a few seconds to get the hardware reset screen. [ok] to proceed. You'll know that the reset is successful if the time and date need setting when you next power the camera up.