This is a very bad warning. The problem could be many things, water damage, hardware failure. But lets go with something you can try. A DFU mode restore. Open iTunes on computer. Connect iPhone to computer. First push Home button and then push Power button, count 8 seconds and let go of Power button, keep holding Home button until iTunes says it has detected iPhone in Recovery Mode, then let go of Home button (usually about 15-25 sec). The iPhone screen should be blank (black), if an image is on screen you are not in DFU mode. If in DFU mode then click to let iTunes restore your iPhone. If not in DFU mode, try to enter DFU mode again. Even experienced users can have a bit of trouble entering DFU mode, keep at it until you get it into DFU, iTunes will tell you when (Recovery Mode window), as long as screen is blank (black). Good luck. Brad