My Sonar X2 Studio won't recongize my Masterkey 49...when I click MIDI instruments the intpur/output boxes are both empty. I made sure teh USB cord is in, and the power is on. Help?

Does Windows recognize it? When you plugged it in, did Windows give you a message that a new device was found? If Windows doesn't find it, Sonar won't either. Look in the Windows Device manager under Audio Devices. If you're using Windows 7 or 8 64-bit, you have to load a 64-bit driver for the Masterkey to work. You can download the correct driver from the manufacturer's website. 

Yes, it works with FL Studio. THe masterkey49 doesn't come with drivers, it's plug-n-play.