Cannot submit forms in Drupal 7
I can suggest how you can test what's happening:


Create custom test form with submit function.  
Install Xdebug on your LAMP, or WAMP or MAMP
Than watch callstack. look what functions have been called.


Looks you've done some specific changes in your instalation.
Also try to download clear drupal instalation and check forms there. 

(P.S. If you have opportunity switch to new instalation).