Instructions
Navigate to the "Warcraft 3" link you use most often. A link is typically created on the desktop and in the Start menu.
Right-click the link icon and click "Properties" to display more information and settings for the link.
Click to place the cursor at the end of the "Target" field. Click anywhere in the field and press the down arrow if the end of text is not visible.
Add a space after the quotation mark at the end of the field, then type "-opengl" and click "OK" at the bottom of the window.
Double-click the "Warcraft 3" link icon to open in OpenGL mode, then begin playing DotA as you normally would.