Hi, I have a problem with a Latitude E7440 Laptop which is sometimes unable to work with wireless LAN.

These are the reported Issues:

Sometimes it fails booting when wireless is physically enabled, at all.
Sometimes it complains about a missing physical wireless device.
Sometimes it comes up but fails to identify the surrounding wireless LANs.
Sometimes it works all fine for an hour and then the connection breaks down.
Sometimes it works after disabling and re-enabling the device in device manager

Bios, Software, Drivers are up to date.
OS is Windows 7 64 bit

What could be the reason
for this behavior?