I'm having a problem with my forum.
All other things (media, resources, social group, admincp, home and others) work.
But forums not.
And when i try to access on the forum, it's slow and appear a 500 Internal Server Error.
Why?
A 500 error is a generic error - the server error log may contain more information to assist with identifying the cause.
Your host should be able to help with that.
Can you ask your host to check the server error log, as mentioned above, and post here its content after your host gives them to you. It can help to identify the cause of the problem.