More information needs to be given. What do you mean by "not working?" Just because it doesn't show up in DXDIAG doesn't mean anything. Do you still have options to configure the switchable graphics through the AMD control panel? If so, have you assigned applications to the "High Performance" settings? If you have done this, and you try to run a game, does the game run better than if you have it set to "Power Saving?" If it does, then your switchable graphics is working fine.
If, for some reason, you notice no performance increase, it is possible that you have the switchable graphics disabled and you are probably on a battery. There is a BIOS setting for that, you can see an example here:http://imageshack.us/photo/my-images/268/79500144.jpg/
For a picture of the AMD Catalyst Control Center configuration screen for switchable graphics, look here:http://h10025.www1.hp.com/ewfrf/wc/document?docname=c03048374&lc=en&cc=us&dlc=en
Edit: Dxdiag, along with Windows Experience Index, is no way to gauge the performance of and functionality of your computer with any switchable graphics. You can get logs from dxdiag that can help solve conflict or driver issues but that's about it.