Quicktime is fine for .mov files, but has too many drawbacks to enable the playing of DVDs,
even with the add-on components - I believe only the basic player is free.
If none of your DVDs will play in say, WMP or PowerDVD or some such program,
the problem lies with your system.
Presumably you have run the usual antivirus / anti malware scans.
If you were previously playing DVDs satisfactorily, with the free space and memory you mentioned,
you'll need to look elsewhere.
Is the drive working correctly with data CDs?
Do your DVDs need a clean?
I've not experienced Mediadirect, but this through Google:
"Control panel>Auto Play>
At the top of page you will see "Use AutoPlay For All Media and Devices",
if this box is checked, click it to un-check it."
Perhaps this will free up your other players.
Edited by petewills , 05 December 2009 - 11:52 AM.