Laptop Graphics Card Not Functioning Properly

I am not really good with computers, I know something is wrong but not really sure how to fix it, I use Windows 7 Ultimate with a dedicated graphics card 2GB GDDR5 AMD Radeon HD 7970M and a intergrated graphics card Intel HD Graphics 4000 installed in my laptop, I used to be able to play Total War Shogun 2 (and other games) with my AMD Radeon Graphics Card, but for some reason my laptop decides to run on my Intel HD Graphics 4000 instead now. With my little knowledge that I have, when I go to device manager -> display adaptors, I can see both AMD Radeon 7970M and Intel HD Graphics 4000 there and my laptop shows that both graphics card are functioning properly (and up to date). But when I go to DxDiag, it only shows the Intel HD Graphics 4000, and when I disable my Intel HD Graphics 4000, my laptop cannot detect any graphics card.