Thread: Upgrade from 11.04 to 11.10 failed

i started upgrade natty oneiric , seemed ok; no errors appeared. restarted system, cannot login screen anymore.
boot messages stop with

code:

mountall: plymouth command failed  mountall: disconnected plymouth

##what did in try find solution
1- tried to login using recovery mode (the system wasn't mounted in read/write mode. so, had

code:

mount -o rw,remount /

2- run update , upgrade, packages installed still same behavior persistent.
3- run

code:

sudo update-alternatives --config default.plymouth

change plymouth's theme (i have disabled splash screen anyway hopeless try)
4- tried reconfigure lightdm

code:

sudo dpkg-reconfigure lightdm

5- tried launch lightdm

code:

sudo lightdm

root shell, system turned blank black screen directly.

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