If you are able to see well enough, in the top left hand corner of Dota 2, click on the settings button. While in settings, you will see different tabs. Click on the tab labeled "Video". Once in the video settings you will see a drop down menu labeled "Display Mode". If you click on the button to drop this down, you will see 4 different options. Clicking on the option titled, "Exclusive Fullscreen", and then clicking on the "Apply" button, will allow you to enter full screen. To return to normal view/to navigate to other windows, simply go back to settings, select "Desktop-friendly Fullscreen" from the "Display Mode" drop down menu, and click "Apply".