If you turned power off it is expected mysqld had no time to remove pid file.
If mysql server starts fine when you rename my.cnf, it confirms that it is having a problem with your file.
Rename the file back to its original name and try starting the server.
Inform us if you still get same error after removing pid file.
Please remove pid file manually, then start mysqld.
$ ls -l /opt/local/var/db/mysql5 total 41128 -rw-rw---- 1 _mysql _mysql 15566 Aug 14 Gabriels-Mac Book.-rw-rw---- 1 _mysql _mysql 771 Aug 15 SDF1.-rw-rw---- 1 _mysql _mysql 5 Aug 15 SDF1.... -rw-rw---- 1 _mysql _mysql 53778 Aug 16 laptop-134....