Login page no longer working

The login page for my wordpress installation at https://youthbuild.cceoinc.org is no longer working. It loads normally, but when I enter my username/pass, it does nothing (not even an error; just goes back to the same blank login page). At first I thought somehow my password had been changed, but when I clicked “lost your password” to recover it, it was never sent to me (I’ve tried multiple times now). So far, I’ve tried changing the password through phpMyAdmin and replacing the wp-login.php file with a fresh copy, but I haven’t had any luck getting it to work yet. The actual site is showing up just fine, but I’m completely locked out. I even tried reinstalling wordpress, to no avail. I’m at my wits end, so any help would be very greatly appreciated. At this point, the only other thing I can think to do is to start completely from the ground up with an entirely new installation and database file, which would be a huge bummer, especially because I do this for a non-profit. Thanks!