Latitude's WiFi connection intermittent. 2 other computers have no problem.

Our Latitude 3550 BTZ with Windows 7 OS, does not maintain its WiFi connection EVEN THOUGH my iPad (sitting right beside it) and our other Dell laptop with OS 7 have no problem doing so. The laptop's own diagnostics point to the router (turn it off and on again: done), so it seems unable to detect the problem.

When the laptop loses its WiFi connection, it shows that either:

a)  It does not detect our WiFi network or

b)  There is no internet feeding into the house...

...EVEN THOUGH the two other computers continue to access the Internet with no problem.