First things first. Log in as root and stop the mysql daemon. Now lets start up the mysql daemon and skip the grant tables which store the passwords.
#mysqld_safe –skip-grant-tables
You should see mysqld start up successfully. If not, well you have bigger issues. Now you should be able to connect to mysql without a password.
#mysql –user=root mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2 to server version: 5.0.22
Type ‘help;’ or ‘\h’ for help. Type ‘\c’ to clear the buffer.
mysql> update user set Password=PASSWORD(‘new-password’) where user=’root’;
mysql>flush privileges;
mysql>exit;
Now stop your running mysqld, then restart it normally. You should be good to go. Try not to forget your password again.