WiFi gets disabled or shut off after sometime.
The above symptom may occur on the following systems:
All Lenovo laptops and All-In-One machines with Windows XP, Windows Vista and Windows 7 installed.
One reason that this symptom occurs is due to power-saving setting. You can try to disable power-saving feature of wireless adapter.
Similar Solution to intermittent break line problem when using Intel 5100 wireless network card has been published on IPS. You can turn to it for further information.