When wiping the display be careful that you don't get debris between the rim and the display. So better wipe from the rim to the center of the display.
I don't really know if this is an issue with the 900 as I own a 600, but I assume that the design will be similar. There were people having their readers stuck because a little something pressed on the screen under the rim and didn't allow for other input (no touch, no buttons).
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