Possibly the drivers arn't updated to work with Windows 8? And is it an official Nintendo GC controller? The disc that came with the adapter worked fine on my system (Windows 7 64-bit).
Windows x64
i7-2670QM @ 2.20GHz
Nvidia GeForce GT555M
DDR3 PC3-10600 DDR3 PC3-12800/8GB Total
Dolphin 3.0-815 x64
i7-2670QM @ 2.20GHz
Nvidia GeForce GT555M
DDR3 PC3-10600 DDR3 PC3-12800/8GB Total
Dolphin 3.0-815 x64
