[ubuntu] On boot, black screen says "Ubuntu 12.04 LTS ubuntu tty1"

hello everyone...
i'm a computer science student, and in one of my courses we using ubuntu on virtual machine (VMware palyer)
the os version is 12.04 and it always ask for upgrade and i delay it, until last night, after the update the machine wouldn't starts,
i got message "ubunto 12.04 LTS ubuntu tty1

ubuntu login: mountall: Discoected from plymoth"
and i have no clue what to do...
any suggestions,?!!!
p.s please explain step by step because i dont usualy use linux.

i want to add two pictures that might help speed up the process.
https://drive.google.com/file/d/0B47...ew?usp=sharing
https://drive.google.com/file/d/0B47...ew?usp=sharing