That's because you're probably typing the wrong username: remember that upon user's creation, if the full name provided it's two words long and it contains uppercases (e.g. "John Smith"), it will default to the first word converted to lowercase (i.e. "john").
Before switching to a
tty, open a terminal within your graphic environment by hitting Ctrl+Alt+t and run the command
whoami: this will return the exact username to be used upon
Since you can't access your graphical environment, try the following:
- Shutdown the system
- While booting, hold Shift to access
Advanced options for Ubuntu and hit Enter
- Select your current kernel's recovery mode (e.g.
Ubuntu 12.04 x.xx.xx-xx-generic (recovery mode)) and hit Enter
root - Drop to root shell prompt and hit Enter
cat /etc/passwd to see a list of all the users present in the system. Check your actual username
resume - Resume normal boot
- Try to login in a
tty using the username recovered from the list