I just noticed that if I insert a DVD, the drive will start spinning but it will not show the mounted disc. If insert a CD, it is mounted, but in some cases it says it is EMPTY CD, but it is not! For CDs it used to ask me what to do with the media inserted. But for DVDs, it doesn't even do that (Also there is some exceptions about DVDs).
This happens with all self-made DVD's I have. Created those quite some time ago on Windows XP with Nero. My DVD player autostarts the DVDs. Windows 7 also plays/sees the files on the DVDs Commercial DVDs open normally, just as self-made data DVDs (old ones made with Gnomebaker), as do audio CDs and data CDs.