Access to Website but not to wp-admin

Okay so I have been working on my website all day in order to further get it ready to go live. However I have not edited any wordpress files only theme related files. But anyhow, I can pull up the website fine and access all the pages, I can even enter the login screen and login, but after that nothing works? I keep getting HTTP 500 error. I can access the site but not wordpress? Any thoughts? The wp-config.php is untouched so i’m not sure what the problem is? Thanks in advance for all of the moderators and volunteers help!