If you have a table in mysql that has crashed and your attempts to repair it using mysqlcheck have failed, then you may have to resort to the lower level myisamchk command.
To use this, you will need to stop the server process (usually service mysqld stop or /etc/init.d/mysqld stop) and then find the data files (usually in /var/lib/mysql/databasename).
You can then run the following command against the table:
myisamchk -r -v -f --sort_buffer_size=128M --key_buffer_size=128M /var/lib/mysql/database/table.MYI
Obviously replacing database/table with the correct database and table.