USB drive won't get assigned drive letter automatically

I had this issue with my computer:
when I plug in any USB drive to my computer, the disk management can see the drive, but it won't assign any drive letter to it. I have to assign the letter manually before I can see the files in it.

To fix it, I disable a service called: SPTD
go to the regedit:
My Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\sptd

change the Start key from 0 (start) to 4 (disable)