Why does my minecraft screen look like this?

You need to full screen it. Find it in option or press F11

It's one of your mods or something, try removing them all

First try making it full screen. If that does not work, pause the game and press the button labelled "Super Secret Settings" until it returns to normal.

If you're on 1.7, go to the options and click super secret settings and check back, repeat this until your Minecraft returns to normal.