ok. try this
1) in control panel - > device manager = uninstall all mouse related drivers
2) detect new hardware
3) stop it from installing drivers (it should be a yellow "!" in the device manager now)
4) download the software from logitech located at this address, matching your OS. Make certain you get the version that matches no only the version of windows but matching if it's 64bit or 32bit.
http://support.logitech.com/product/11383
5) run the install program as an administrator
if it doesn't work after that...
6) check the device manager and see if the mouse is still highlighted with a yellow "!"
7) if it is, right click on the device and select install driver
-chose to "browse your computer for the driver"
-then chose "let me pick from a list of devices"
-chose mouse
-chose logitech
find the LATEST driver listed for the G502 mouse (there might be several listed for this mouse. if this one doesn't work, try another)
7b) if it isn't, then uninstall the drivers the mouse is using, detect new hardware, then chose
-"browse your computer for the driver"
-then chose "let me pick from a list of devices"
-chose mouse
-chose logitech
find the LATEST driver listed for the G502 mouse (there might be several listed for this mouse. if this one doesn't work, try another)