Win 8.1 Logging off instead of shutting down, and showing "Airplane mode ON"

Okay this is a very weird problem. This computer is a Dell Vostro 3558, came with Ubuntu, which I removed, tued off secure boot, switched BIOS to legacy, changed HDD to MBR, and installed Win 8.1 Pro (x64).

I generally use a USB 3G modem to connect to the inteet - hence didn't get to test the WiFi adapter right after purchase, but from a week or so I'm using my phone's inteet sharing over WiFi option to connect this notebook.

Say I connect to the inteet over WiFi, it's working fine, now after a while I click on Shut Down, instead of shutting down, Windows logs me off and retus to the "Enter password" screen, and a popup flashes on the top left coer saying "Airplane mode ON". Say I click on shut down again, it flashes "Shutting down" for a fraction of a second, and again retus to the "Enter password" screen, this time saying "Airplane mode OFF"... The cycle continues ad infinitum- the only way to exit out of this loop to click on "Restart". If I click on Restart, it shuts down, shows the "Dell" BIOS logo, the Windows logo, and starts up. Now if I log in, use the computer for a while, and shut down again, it will shut down fine. But after a few power on- shut down cycles, the problem retus, and I have to "Restart" again.

This is an extremely weird behavior, and this is the first time ever I have encountered something like this.

If it matters, my phone is a Lumia 925 (Win 8.1 Update 1), and the WiFi card in the computer is an Intel AC3160.

Installed the latest WiFi driver from intel.com, but the issue persisted. I have since retued back to the driver available on dell.com

What could be causing this?

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