F14 to F15 blocked on reboot ... :-(

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http://forums.fedoraforum.org – Hello. For Upgrade from F14 to F15 I used Preugrade. During the PreUpgrade all worked fine then the system was rebooted to complete installation. The current problem is that the reboot process seems to be blocked (since already a long time !) with the freezed display enclosed in attachment (I do not how insert image in this text !). The picture in attachment is just an exemple that I found on web, but currently it is not freezed on the same libraries ! I am a little scarred because this is a dangerous stage ... and I do not know what can I do in this case !!! I will be very grate (HowTos)