ok - not in front of a windows PC at the moment so going from memory
exit cubase
go to:
C:\Users\XXX\AppData\Roaming\Steinberg\cubaseXXX - with your windows username and the cubase version instead of XXX (obviously!)
there is a file in there called something like mediabay3.db ? (I THINK!)
rename it to mediabay3.bak
restart cubase…