facing lightdm problem

i just changed lightdm background picture thats why i seems a pretty big problem on my netrunner desktop,now lightdm does not run on loginscreen it shows some error messege :@

What error message ? Maybe the background image path you set isn’t available. Please double check that.
Otherweise you can reinstall netrunner-system to set it to the default again.

hum maybe.but how to double check the path i am newcomer about netrunner and how to reinstall netrunner-system and how to set it default.Brother i just changed loginscreen background from system-setting.now netrunner isnt starting and it shows http://oi43.tinypic.com/2i1miq9.jpg
please please help me brother

Do you have access to a tty ? (CTRL+F1 , CTRL+F2 …)
If you have you could login with your user there.
And then try the command startx to start the graphical user interface.
If that works please try resetting the lightdm settings (so set it back from the systemsettings).
Then try rebooting.
If that did not the trick, then please try reinstalling netrunner-system with muon packagemanager.

Thank you brother it helped me,.,.,.,.
Now brother another problem,i like ubuntu softwar center so i installed it but it doesnt work!please get me solve About this installation.Huh