I had a nice refurbished Elitebook 2540p come back after a day because the WiFi somehow got turned off and the customer couldn’t turn in back on. Pressing the WiFi button over the keyboard did not toggle the WiFi back on as it was supposed to. The drivers looked fine and reinstalling them did not solve the problem. Bluetooth may also have been having a problem.
This is related to the HP Power Assistant Tool which apparently “helpfully” decided to turn off the WiFi when the customer’s battery got low but wasn’t helpful enough to turn it back on when it got plugged back in. I tried to manipulate the controls on the tool in some way that would get WiFi to work again but all I could succeed in doing was toggling the Bluetooth. Finally I uninstalled HP Power Assist, but unfortunately this only seemed to have left the WiFi in a permanently off state. I could now get the light to go blue but this only turned on the Bluetooth and not the WiFi.
I considered re-installing the (stupid) HP Power Assistant but instead decided to test whether I could get the WiFi going outside of Windows. I have a Linux Mint live disc and booted off of that. Sure enough, the WiFi ran fine under Linux. After rebooting into Windows, the WiFi worked just fine. I will not be re-installing HP Power Assistant.