Wifi Shut-off after a couples of hours, help!

Hello,

I have problem with my acer 4720z wifi shut-off automatically and the light stop blinking always light on, when i check the hardware/device manager no network adapter installed, when i re-booting the laptop the wifi works again but after a several hours the problem back again automatically shut-off, i really tired to install a driver over and over again but the problem still persist, what can i do? can you help me?