I hope this answer helps others. I fell asleep watching something on my tablet. The battery alert woke me, so I plugged it in until it was fully charged. When I went to use it the screen was very dark, but everything seemed to work okay. I tried everything, searched through all the settings looking for screen brightness, even deleting some big files in case the memory was full. Then although it was really hard to see what I was doing, I pulled down the drop down box that has the summary of the functions (time, day and date, wifi icon, location icon, sound icon etc.) and just below those is the screen brightness bar which was at its lowest. As soon as I moved it, the screen lit up as normal. I must have shifted it while asleep. Lizzie