[exalos]

This is because of the macrovision protection.
Just do a search on how to remove macrovision.
As I understand you haven't got a DVD-ROM at your pc, but you have a separate one to watch on the TV.
My opinion is that if you want to back up DVDs you should buy a DVD-ROM and do the whole thing at the pc!
It is a lot more easier and cheaper too. It is cheaper because you do the whole operation (backing up the dvd) whith programms that are free to use, and you won't have to buy any hardware (to bypass the macrovision protection) as you'll probably need if you don't buy a dvd-rom.