I awoke in the middle of the night and tried to power on my Tab in the dark and to my surprise I got a screen with an android digging inside a triangle with the message "Downloading Do not turn off target!!!" I waited to see if anything happened and meanwhile I Googled for help on my Laptop and found many suggestions including: removing the battery (not easy), connecting to the PC and using Kies, ringing Samsung for help, returning the Tab to dealer because it was bricked etc. Eventually, on Xdata I found the answer which was to hold down the power button for 10 seconds which cleared the downloading message and allowed me to power on normally. I think I may have accidentally pressed the volume and power on buttons at the same time which produced the downloading screen. I thought I would share my experience to help others with the same problem.