First, what Operating system do you have?
If you have Windows 7:
1. Click the windows button on the task bar.
2. Right click computer on the side of the thing that just popped up.
3. Select Properties
4. Scroll down and list everything you see(Notable your Graphics Card)
I just noticed that doesn't tell you your GPU.
But I know you have to do something with the cmd prompt, but I forgot what the console command was.