As you are unable to access your DE another solution would be to use ctrl+alt+f1 to got to a tty login.
login as your username
locate and highlight the .dmrc file for the user
press f9 for the drop down
use the arrow keys to navigate to 'file' then select 'Chmod' and use spacebar to uncoment the read/write/execute by others sections (ie you own the file and are the only one that can write to it)
once done select set and save the change , then press f10 to close mc
once mc is closed, use alt+F8 (try F7 also) to return to the gui login, restart X by using ctrl+alt+backspace then try to log in
This should solve the issue