How to re-enable Windows user options pop-up for newly mounted USB Flash drives?
Go to:
Control Panel
> Hardware and Sounds
> AutoPlay
Or more simply, click on Start
> Type autoplay
and press Enter
Put a check on Use AutoPlay for all media and devices
to make that AutoPlay popup-dialog appears for you again when you insert a external media device.
You might need to reboot your computer in order for this to work.