I've done that a million times. No luck. I do have some progress though: I read about holding the home button down when reconnecting it to the computer and it restarts and goes to a screen showing the cord hooking up to Itunes. Itunes on the computer then sees the machine and says it needs to be restored. Warnings come up that it will be wiped out, which is fine with me. It tries to restore it for about 2 minutes, the phone restarts itself and then itunes says it can't be restored, that error 21 is causing it to not be able to be restored. I read about all kinds of things to do, be sure it's the only USB device (besides my keyboard and mouse) and be sure it's hooked into the back of the computer, not the front, restart the computer. No luck, still error 21. Nothing I do on the phone changes the screen except I can hard boot it with the top and home button held down. Still just goes to the iphone connection screen, whether or not it's hooked up to the computer or just the AC charger.
HELP!!