Nobody in the forum can login

[MistViper]

Hey guys I have a pretty big issue here. On my forum whenever I try to login, or any other user tries there is an error. It says invalid username/pass and that we need to wait 15 minutes before trying again. Do you guys know any way to fix this? I've seen people say go to php myadmin and create an admin account, but will that work for this issue? I'll try it and let you guys know but if you have ANY other help that would be greatly appreciated. Btw the site is -> mistviper.com

Edit:

I get this error when installing the tools.php file to my admincp directory:

Warning: require_once(./install/includes/class_upgrade.php) [function.require-once]: failed to open stream: No such file or directory in /home/mistvipe/public_html/forum/admincp/tools.php on line 46

Fatal error: require_once() [function.require]: Failed opening required './install/includes/class_upgrade.php' (include_path='.:/usr/local/php53/pear') in /home/mistvipe/public_html/forum/admincp/tools.php on line 46