MySQL Performance Issues (1 reply)

I am running
2x 2.1GHz AMD Opteron™ 12 Core processors (24 cores)
32GB RAM
Ubuntu 9.04
2x 300GB SAS + 2x 500GB SATA hard disk drives

My problem is I have a vbulliten site that just crawls. I have looked and seems mysql is the problem. in top I see my CPU maxed. It seems to be only using 1 core. My config file is as follows.. Anyone have any suggestions to help me. This site gets about 15-20k hits per day so nothing super hard.

[mysqld]
back_log = 50
max_connections = 1250
key_buffer_size = 1536M
myisam_sort_buffer_size = 256M
join_buffer_size = 2M
read_buffer_size = 2M
sort_buffer_size = 4M
table_cache = 5000
thread_cache_size = 768
wait_timeout = 40
connect_timeout = 10
tmp_table_size = 128M
max_heap_table_size = 128M
max_allowed_packet = 64M
net_buffer_length = 16384
max_connect_errors = 10000
thread_concurrency = 16
concurrent_insert = 2
table_lock_wait_timeout = 30
read_rnd_buffer_size = 2M
bulk_insert_buffer_size = 16M
query_cache_limit = 8M
query_cache_size = 512M
query_cache_type = 1
query_prealloc_size = 262144
query_alloc_block_size = 65536
transaction_alloc_block_size = 8192
transaction_prealloc_size = 4096
default-storage-engine = MyISAM
max_write_lock_count = 16
ft_min_word_len=3
user = mysql

innodb_data_file_path = ibdata1:50M:autoextend
innodb_data_home_dir = /var/lib/mysql/
innodb_log_group_home_dir = /var/lib/mysql/
innodb_log_arch_dir = /var/lib/mysql/
innodb_buffer_pool_size = 384M
innodb_additional_mem_pool_size = 10M
innodb_log_file_size = 100M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 1
innodb_lock_wait_timeout = 50

pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.sock
port = 3306
basedir = /usr
datadir = /var/lib/mysql
tmpdir = /tmp

[mysqld_safe]
nice = -10
open_files_limit = 8192
[mysqldump]
quick
max_allowed_packet = 16M

[myisamchk]
ft_min_word_len=3
key_buffer = 64M
sort_buffer = 64M
read_buffer = 16M
write_buffer = 16

Thanks