Users and Admin not able to login to drupal site - redirect loop

On one of my websites, I had this weird issue one day suddenly . Both users and admin was not able to login to website. It was going into redirect Loop and it used to display page not found "404" or it used to just be on the login page. I read in forums on and several other pages. There were many solutions proposed, which were actually quite confusing and not convincing I had not changed anything on my website to cause this issue, they why suddenly no-one is able to login.

Instance 1:

The fix came from one of the comments "All I HAD TO DO WAS REPAIR THE "sessions" table" in my phpmyadmin.

repair table sessions 

This table was getting locked out due to some looping activity. I did have persistent login module on my website, which I disabled. Once I executed this repair statement in my database, users were able to login just fine.

Instance 2:

Another instance when I had this issue was when I migrated from Drupal 6 to Drupal 7. After doing some updates, I was not able to login to drupal tried every possible option. The issue was some of the updates for contributed modules did not complete. 

Run update.php again if you are in this situation. Remove the contributed modules for which it throws error. 

Following did not work

ini_set('session.cookie_domain', 'exampleorg');
ini_set('session.auto_start', 0);