I think that most likely you have a problem with the file access rights for the sound files. To check that please do following:
Open a command shell (cmd.exe) and copy and paste the line
icacls C:\ProgramData\Steinberg\Content\*.* /T >> %userprofile%\Desktop\SMTGContentsAccess.txt
Hit the return key and after a couple of seconds on your Desktop the new file SMTGContentsAccess.txt shall appear. That file please post here. Thanks