- Can you switch to a console with [ctrl + alt +F4] ?
- Can you login (there) using your username and password ?
- Or can you only login as root ?
(May be your login is rejected,
- because the system thinks this is not the correct password, or
- because the system thinks you have tried to often
)
As root you can give your user a new password that may work
Did you run startx as root ? (don´t !)