Scenario: You boot into Windows and see that some drives do not have a drive letter assigned and thus are not visible in the Windows Explorer.
First please note that we do not encourage or support interferences to the WIndows registry. If you make changes to the registry you should know what you do. Failures can damage your system.
Please check the value of the registry entry HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\mountmgr. The value of the key “NoAutoMount” has to be 0. If it is 1 this can cause newly attached devices not to get drive letters assigned.