Need...Help...Bad

Okay, i absolutely don't know what to do...

I enter: mydomain.net/admin

(From the demo that i tried, it should have gone to the admin login.) Which...it didn't (It gave
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.)

, so i tried domain.net/admin/admin_login ... i tried logging in there and then it it gave me this

Not Found

The requested URL /admin/__action_url__ was not found on see more this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

So...I don't know what to do after that...I want to get in admin, so i can take out that image security feature...

Anyone got any ideas? Please help.