Startup loop

Hello, I have a BIG problem since yesterday. My computer doesn't start. At the welcome screen, it says "Loading your personal settings...", then the desktop background flashes and it says "Saving your settings...". And it does it again : Loading your personal settings, Saving your settings, Loading your personal settings, Saving your settings.

I tried to go on Safe Mode but it does the same thing. I tried the Safe Mode with network and command prompt. Still doesn't works. I tried Debugging Mode, I tried everything on the F8 Menu. Does someone knows what to do, without formatting ?

Please. Thank you