Let's see if I can help.
Check the if the Media is a -R or +R and make sure that your drive is supposed to be able to read it. By the way - I've had some problems with the cheaper LG drives reading +R DVD disks.
Please do a simple test to help us narrow this down a little (i.e. to verify if the problem is a) the disk or b) the DVD device or system.
- Burn a data DVD in your DVD burner and see if it can then read it (or will burn at all).
- Burn a data DVD on another computer and see if your computer can read that disk.
- Try the disk that you can't read in another computer, does it read it correctly? If so is it the same type of DVD device (LG etc)?
If you prove that the problem is the disk you may want to look at a DVD data recovery program. There are a number of free ones around.
Consider also doing a serch for the latest drivers
for the DVD device on the manufacturers website.
Lastly, my golden rule that I tell all of my clients is to NOT store data on CD/DVD media they too often become corrrupt.
PS: An afterthought - Could it not just be a previous sessions data on the disk that was never closed (i.e. it could just be crap left over from a bad burn)? OR have you actually lost data?