Once mine finally downloaded the update my prime seemed to of hung on the Asus screen as well on its first reboot.. I wasn't paying 100% attention to it at the time so it probably sat on the screen for 5 minutes with out any sign of updating.. I thought OH NOES! reached up tapped the power button to see if the screen would go off and instead.. it finished whatever it was doing and continued the reboot and went on to install the update.
Either I got lucky.. or something interrupted / corrupted your update