Seems like hildon-desktop is crashing, most-probably because of bad/missing transitions.ini. You can try to start xterm using ctrl-shift-x right after reboot (while hildon-desktop is still alive). Could take a couple of tries though. Once you have running xterm you can check transitions.ini in /usr/share/hildon-desktop. Also there was reports that older versions of CSSU Configuraion Application messes up transition.ini. Another thing to care of is if you have installed a theme which has its own transitions.ini. Anyway, once you have xterm running I think you should be able to solve your problem without reflashing.