[ubuntu] HL-DT-ST-GS20N reads CDs, not DVDs

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http://ubuntuforums.org – I'm new to Ubuntu and very confused. I installed 64-bit Ubuntu 12.04 on a Dell Studio XPS 13 (1340). I have a slot loading CD/DVD drive that will mount a CD, but not a DVD. The drive is a HL-DT-ST-GS20N. When I insert a CD, it spins right up and mounts. When I insert a DVD, it doesn't even spin. The drive works with windows, so I don't think it's a hardware issue. I would greatly appreciate any assistance. Thanks in advance! (Hardware)