How can i Deactivate the user In asp Dot Net?

you can create a column in the database for the number of login attempts and another column which says date-time of last attempt, when the user is loging in, you can increment the update login attempt column and also update the last attempt with current date-time. Once the value in the column reaches 3 you can inform the user that he should try after 24 hrs. Write a script in the database or c# schedule it to run every hour or so and update the database column value back to 0 where the last attempt has past 24 hrs.