Non filing of itr

hello friends... These days most of the people are getting letters from the department for not filing of ITR. After getting this one should file the return with appropriate info. Now i want to ask that in case we can not file return of a particular year,then how to reply.??? suppose i get a notice at this point of time for non filing of ITR for ay 11-12,12-13,13-14. now i can not file ITR for Ay 11-12,12-13. and tds was also deducted in those years. How should i manage it....??? Also tell me possible solution if i received letter online on my income tax portal in 'compliance submit'. thanks