windows 8 wifi keeps disconnecting from internet but stays connected to router

Hi

system = Latitude E6330, windows 8 pro, 8GB RAM,

system will maintain a wifi link to the internet for a few minutes then drop the internet connection but still remain connected to router.

have changed advanced adapter settings so that power saving does not stop the wifi adapter. But the problem still persists.

any help and guidance would be welcome.

thanks

rich