@sdiox: broken displays look fine from the outside, except that the displayed image is not 100% perfect. Not sure what looks fine to you and what not in that regard.
If everything looks fine it's an odd issue since all other damages (even bad sectors in the internal memory) tend to blank the display in any case on power off/on. Maybe the display cable came loose internally? Highly unlikely for that to happen on its own though.
If it has an internal SD card slot you could try replacing it... *shrug*
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