Okay. Reading through this sorta fast, at work, you have to turn off the the Dell forcing the Intel HD on board GPU in the Bios. http://en.community.dell.com/support...519/t/19586281
Now, it's an older thread but, it will explain the issue you are having. As soon as I saw this thread I had an idea that was your problem. This is why LTs are not the best for gaming. Sure, you can have dedicated GPUs blah b;ah blah but, when they crap the bed, you're S.O.L. for replacing them.