Themes And Edit buttons Are Scrambled

Hello, im having serious problems here.

1. For some reason every theme that i download have a scrambled heading with mixed colors as you can see by clicking Here. The only themes i can use is the classic/default themes that came with wordpress installment. Before someone told me that the code was repeating itself, but what code?

2. My edit buttons looks like someone took a pen and scribbled over them. My media for pictures or video is gone, but then i noticed this black line drawn under my edit buttons above my writing post which is “THE” link for my media pictures and video. The crazy thing about that is i cant even write a post because that media link is totally covering it.

3. Login section: The title of the login section “WordPress” is covered with a black banner…do that have anything to do with my theme problems also. If anybody can help me out with this it will be so appreciated. Thanks so much!