Settings for DVD-ROM

This is going to sound silly, but I'm going to ask for help anyhow.

Some time ago in an effort to access the ROM features on a DVD disc, I changed my drive settings from DVD-video to DVD-rom. A few days later I went to play a DVD movie and found that no matter which media player I used (Nero Showtime, Windows Media Player) the video played at double speed and I cant for the life of me find where I changed the settings! I've checked in device manager and hardware settings but I just can't remember where it is. Please advise.

I've got a Dimension 4600 Running Windows XP and a Hitachi DVD-rom and Sony DVD-RW.

Thanks, John