One of the reasons for this could be the hacks that are installed in the forum.. You might want to try to disable the hacks, one at a time to see if it's a particular one...
Also try this:::
Also try this:::
Login as root
Then run mysql -u root -p
Enter your password and run
mysql> show processlist;
This will display the current active queries. Look at the queries and look at which ones are taking the most time They are probably hogging the cpu.