Not much to say about that. I've seen many similar questions but didn't solve the problem. Animation plays fine. It was visible earlier and I didn't do practically anything except switching views and trying some menu options.
You have "pushed down" the action and created a strip. Select the strip and press the Tab key to tweak it. As the manual says:
The contents of Action strips can be edited, but you must be in Tweak Mode to do so. The keyframes of the action can then be edited in the Dope Sheet.
EDIT Also see this question: Can action strip converted back to keyframes?
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$\begingroup$ Thanks. More precisely I need to not only have action selected but It must be last thing clicked (otherwise Tab switch lock/unlock). I actually even remember I did something like "pushed down" but it is unfortunate that I can't reverse it with similar move - I didn't want to use NLA, just see what it is... :) $\endgroup$ – Paweł Audionysos Dec 11 '16 at 17:41
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$\begingroup$ It can be kind of reversed, see the link in the edited answer. $\endgroup$ – lbalazscs Dec 11 '16 at 18:05