When Autoplay system settings changes still do not work try the following to fix a corrupt registry and reset functionality:
Applicable for Windows 7-10 - copy the following into an editor:
Windows Registry Editor Version 5.00
and save it with the extension ".reg" (f.e. "autorun_restore_fix.reg") and run it - answer with yes. (Or run "Regedit" and edit the values in their proper keys as shown above). No need to reboot: changes to HKCU are immediate.
Hint: XP also can use the .reg file, just replace Registry Editor Version 5.00 with 4.00.
Alternatively, you can completely remove the following Explorer key from registry:
...if there are no other values in it and you don't need specific users policies.
Don't worry: there is no "Explorer" sub-key at default Windows installation, so it's safe deleting it. This will make the USB autoplay action requester pop-up again as well, resetting it to defaults.