DVD read problem?

I have a DVDROM rom that is playing vcd's perfectly but when I try to play a purchased dvd nothing happens,I've checked the region settings and they are fine,I'm getting no error messages either,they just won't play,the software I'm using is win dvd4. I've reformatted the comp,checked all my settings ,cables etc,still no go on a purchased dvd. The drive is a Lite-on.

is the drive new??? has it ever played any dvd??? i'm saying this because a couple of years ago i bought a dvd kit from creative (encore 5x which included a DVD-rom drive and a mpeg2 card) the drive was able to read cd's, but it wouldn't play dvd's.

You sure it's really a DVD and not a CD? ;) I've had a DVD that wasn't able to read DVDs, only CDs. Luckily because of the guarantee it was replaced without any cost.