It sounds to me like your Graphics Card is not recognized by your computer. If you know how to access your System Settings through Bios, you can check there to see if your Graphics are identified. One very easy way to see your Graphics recognition is to download and install CCleaner. It will show your available Graphics at the top left of the Application window. It will also describe your CPU and Memory.
Most likely, you did not reinstall your Drivers for the Graphics Card in your Alienware machine. Go to the Alienware website and find the driver(s) needed for your computer. You might consider getting Automatic Updates from the manufacturer of your machine.
After you have reinstalled the Drivers for your computer and/or Graphics Card, Restart your computer and see if your Graphics are present. Since you have changed the Hardware Profile of your Alienware computer you should check all of the Settings and adjust them as necessary.