need help!!!trouble with logging in

Hy allz!i have a problem with somebody's forum...i can't log in on his forum,even i have an account...when i select connexion or log in the page with user and password dind't shows...he shows me the homepage...what can i do? is some setting that he made probably a mistake?or....something else? please contact me!cause i really need to enter on that forum!i must help him with the administrators commands...and i can't do this without loging in (...please help me!thanks for help and hope to get an answer as soon as possible