Please download and install the following driver for your mouse under Windows 8.
http://ftp.hp.com/pub/softpaq/sp60501-61000/sp60674.exe
Once the driver is installed:
Plug in the wifi mouse dongle. Ensure that the dongle you have plugged into a USB port is the correct one for the wifi mouse. Wait for the sound that indicates that the OS has recognized it and installed the driver.
Once you have done that, you can press the button to pair the mouse with its dongle.
Are you connecting the dongle to a USB 3.0 port?