Forum Can't log in...?

[محروم.كوم]

OK, yet another blank-stare problem. Files uploaded, install procedure completed, install.php and all upgrade*.php-files deleted, log in to cpanel pop up, enter username/password, "Thank you for logging in *username*" pop up, return to log in page. The damn thing won't let me log in.
Now, some extra background:

My first install I uploaded the "upload" directory itself, so the address to the forum became *domain name*/*my name for the upload directory*
Everything worked fine this time around.
But since I only have the forum on this domain, I want people to be able to enter the domain name and find the forum. So I deleted the files and redid the install, this time uploading the files IN the upload folder directly to the public_html folder. This time the install worked just fine and I get as far as the log in page, but it doesn't log in. It tells me I'm welcome and then throws me out. Oh, I've tried redoing the installation a few times and tried all the suggested cookie domains (.*my domain name* and blank); no can do siree.
Please, is there anyone here who can tell me what the heck is going on? __DEFINE_LIKE_SHARE__