My HL-DT-ST DVDRRW GSA-H20L will play CDs just fine, and will also play burnt DVDs and a very select few purchased DVDs, but 99% of DVDs I've tried to play don't work at all (absolutely no reading of DVD material, nothing in explore DVD-drive and no prompts to play the DVD). It's like I've open the tray and then closed it again. Any help with this problem would be much appreciated.