I can play 1 Charlie Brown DVD, but no other purchased DVD's.  I am running Windows XP Professional, Optiplex 240.  I have Dell's PowerDVD with the patch installed.  I updated the firmware for my CDRW/DVD Samsung drive.  I have checked all drivers for the IDE ATA/ATAPI Controllers to be sure they are updated.  I am running Region 1 for DVD's.  Transfer Mode is set to DMA.  I have checked all DVD's and they will run in my old computer.  I also downloaded an updated version of PowerDVD  as a trial and obtained the same results.  I am at a total loss . . . Any help appreciated.