Cause of crash: Disk full.

when you try to start MySQL using this command:

/etc/rc.d/init.d/mysqld start

it failed to start.

So you check log file:

tail -100 /var/log/mysqld.log

and you see:

071120 18:36:06 mysqld started
InnoDB: The log sequence number in ibdata files does not match
InnoDB: the log sequence number in the ib_logfiles!
071120 18:36:06 InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
InnoDB: Last MySQL binlog file position 0 110344596, file name ./mysql-bin.000082
071120 18:36:06 InnoDB: Started; log sequence number 0 3039427084
/usr/libexec/mysqld: File './mysql-bin.000082' not found (Errcode: 2)
071120 18:36:06 [ERROR] Failed to open log (file './mysql-bin.000082', errno 2)
071120 18:36:06 [ERROR] Could not open log file
071120 18:36:06 [ERROR] Can't init tc log
071120 18:36:06 [ERROR] Aborting

071120 18:36:06 InnoDB: Starting shutdown...
071120 18:36:09 InnoDB: Shutdown completed; log sequence number 0 3039427084
071120 18:36:09 [Note] /usr/libexec/mysqld: Shutdown complete

071120 18:36:09 mysqld ended

Easy fix: open mysql-bin.index, delete all content in the file and restart MySQL again.