excel2345

I have installed and can create an affiliate account, from there emails are sent with credentials and I can login and see the various items available to my will be affiliates. I cannot log in to admin, I get the login screen and using the admin credentials sent to me when I installed it just goes back to the login screen, no error messages or errors. I have edited the htaccess file to rewrite. Does anyone have any ideas as to what is wrong? Thx Bill