== I’m using BP 1.5.1, I didn’t have problem until days ago ==
Did you just upgrade and/or install a new theme or plugin recently?
Did you go through the Installation Wizard?
Have you gone to dashboard menu BuddyPress > Forums > Forums for Groups – and clicked on Use Existing Installation?
Hello mercime, thank you for your assistence..
No, I didn’t make any upgrade in this month.. nor installed a new plugin.. My forums worked good before..
But I have some changes because my site was hacked, and this affected the Buddypress default theme: all my index.php files receive a malicious code.
I cleaned all files, changed my passwords, etc… When I saw the problem with the forums (today) I reinstalled all Buddypress files.. but the forum doesn’t work.
I used Installation Wizard when installed Buddypress.. Any idea?
In the WP admin dashboard, try navigating to “BuddyPress > Forums”.
Under “Forums for Groups”, try clicking on “Install Group Forums”. If you don’t see that, click on “Uninstall group forums”, then you should see the Install Group Forums button, click on that button.
Next, under “BuddyPress > Components”, make sure that “Discussion Forums” is checked.
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If that doesn’t work, it could be a database problem. Try logging into phpMyAdmin and repairing your tables.
Also make sure that the following tables exist and have data populated in them:
* wp_bb_forums
* wp_bb_meta
* wp_bb_posts
* wp_bb_terms
* wp_bb_term_relationships
* wp_bb_term_taxonomy
* wp_bb_topics
After long time and many tests, I found the problem: when my site was hacked, I changed all passwords… all? No! I forgot a password in bb-config.php.. (holy shit..!). I erased the old user then bbpres can not connect to database.. The system doesn’t says nothing for me, no error message, no blank page.. just doesn’t shows my foruns… rs.. I really sorry about this.. thank you..
No worries. Glad you you resolved this on your own 
