If You are facing problem with Unknown table engine 'InnoDB' on to your mysql Database. You can do following to get rid of this problem. First look at the ib_logfile0 and ib_logfile1 in /var/lib/mysql. If they have been set to size different from the default, that probably will prevent mysqld's startup. The default for innodb_lkog_file_size is 5M. Add this in my.cnf 
[mysqld]
innodb_log_file_size = 12M
And then Proceed by doing following 
/etc/init.d/mysql stop

mv /var/lib/mysql/ib_logfile0 /var/lib/mysql/ib_logfile0.bak # these are your
mv /var/lib/mysql/ib_logfile1 /var/lib/mysql/ib_logfile1.bak # log files

/etc/init.d/mysql start
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