mysql ibdata1 corrupt
If you don't have backup.

I think the recommended way to recover that databases is start MySQL with innodb_force_recovery = 4 (or higher values) and dump the databases to a SQL.Then drop it and recover from backup. Instead of dropping the original database I prefer to create the new databases with another name or in another server and check the content first.

STEPS TO BE FOLLOWED


In mysqld section of my.cnf add a line innodb_force_recovery = 4  and then restart MySQL server using /etc/init.d/mysql restart.
Take backup.
Restore it on other server and verify the contents.


Please also have a look at Forcing InnoDB Recovery.

UPDATE : For your comment how to progress on that so that it would not happen again

You should not kill MySQL it is not a good practice that may cause MySQL server to crash,whenever you make any configuration changes you should proceed as follows.


Safely stop MySQL Server using /etc/init.d/mysql stop
Make changes 
Restart MySQL Server