If the button will not load while the PC is on, you can try using the Assist button while the PC is completely shut down to see if the hardware partition is still intact.
Unlike standard USB or audio drivers, the Assist button relies on a complex chain of proprietary Sony software layers. If you format your hard drive or upgrade your operating system, Windows will install generic drivers. These generic drivers lack the code required to recognize the specialized hotkeys on your laptop shell. sony vaio assist button driver download link
first and restart your computer.