Same thing happened on my old Asuspro - new SSD and Windows 10 addeda few years ago. No amount of hard booting would get rid of the blue password box???? Took the battery off - noticed ‘Lock’ slider wasn't over, thought nothing of it. Powered on and there's my Windows desktop exactly as it was, even browser windows open!! Replaced battery, locked it on ? and everything's good again. No I have no idea either ? just happy I don't need a new hard drive.

Been having the annoying red x / slow charging / trouble turning on issue on my Tab 10.1. Thanks for all the suggestions, obviously a known issue!! Tried many leads and Samsung plugs but made no difference. What worked for me - holding down the power and volume buttons for about a minute. The Samsung Galaxy Tab 10.1 logo flashed up every 10 seconds or so. When I let go it started up normally and there was a white lightening flash on the battery icon as normal. Thanks guys