ERROR 1045 (28000): Access denied for user 'ashwini'@'localhost' (using password: NO)

I've installed the LAMP stack on my Ubuntu 14.04 . when I try to run mysql, it shows the error :

ERROR 1045 (28000): Access denied for user 'ashwini'@'localhost' (using password: NO)

I've tried reinstalling the LAMP stac, MySQL, and tried all the possible things. But at last, i get the same error. Please tell me how to come over this?