Can't Change Settings

So on my settings page in the dashboard, I can’t make it so anybody who comes on my website can register an account. Whenever I go into the general settings page, and try to save any settings. I get a 403 error: Forbidden.
It isn’t my host because it worked perfectly fine with previous versions of wordpress. However this is a major problem as I want users to be able to login so they may use forums and such.
So if anyone could help it would be greatly appreciated. Thanks.