Check the event viewer for reported errors.
This freezes started to happen after that I tried to change the folder pictures of the hard drive in 'Computer' folder. The icon (picture) is not changed, but it started to happen above. Everything returned to normal when I did system restore points in an earlier time.
It seems that the folder picture of the drive can not be changed (or are not allowed in the regular procedure).
In any case, thanks for your reply.