Cant set graphics above "Medium"

[Phrazer]

Hi guys, very sorry if this has been asked before, I did do a couple of searches but to no avail.
Basically I cant set the graphics above Medium in the graphics options page, only Low and Medium are options... is this a common problem?
Ive got a Alienware m17x laptop so I wouldnt have thought I would have many problems running it, but I dont know. I cant remember the exact specs its got, if you need to know them to answer my problem ill post them later when I get home. I know its got a quad core processor and 12gb RAM but I cant remember the specifics off the top of my head!! lol.
Many thanks for any help.

[A Barbarian]

Maybe you don't have a DX11 compatible graphics card. See whether you can change the 'Shader model' setting on the graphics page. Shader 3 is DX9, Shader 4/4.1 are DX10 and Shader 5 is DX11.