When I plug any USB key - which does not include mice using usb ports or any hardware whatsoever, it shows for a few seconds and then disappears and then just starts flashing making my system go insane.

This does not affect my alternative user account.
If i'm quick enough to enter the USB key, the window closes.
If I am quick enough to enter the USB key and open a file, it does not close and USB stops flickering.
Using Windows 8.1

Possible cause:
Registry issues