If your graphics card supports this feature, you should be able to rotate the display with the key combinations:-

Control + Alt + Right Arrow 

Control + Alt + Left Arrow

Control + Alt + Up Arrow

Control + Alt + Down Arrow

As was said, you need a graphics card that supports this.  Your generic built-in (integrated) graphics chips will not typically allow this.  I use a Radeon HD2950 Pro and it does this - however, it's a touch pricey.  You can get an ATI card for about 50 bucks that will do this.

Thank u so much. I really apprciate it. This really helped me alot.