"Error 1067: The process terminated unexpectedly" when trying to start MySQL

Examine error log (start eventvwr.msc). MySQL typically writes something to the Application log.

In very rare cases it does not write anything (I'm only aware of one particular bug http://bugs.mysql.com/bug.php?id=56821, where services did not work at all). There is also error log file, normally named .err in the data directory that has the same info as written to windows error log.

You need to:

1. stop the MySQL service:
2. Open mysql path\data
3. Remove both ib_logfile0 and ib_logfile1.
4. Restart the service