More than likely , It's the USB of your PC . A PCs USB port is simply not as fast or reliable as MAC USB . I build both computers and I have found this to be true , I use my USB with audio and MIDI in my 333mzh IMAC and have no troubles what so ever . So rather than get into some meaningless MAC VS PC war , try using using one of your PCI slots . The PC USB is simply not good enough .