I have a Dell Precision 390 running windows 8 consumer preview, with an HD 6670. The disk drive won't read newer games, but can read and install older games and ones activated on steam. Should I just buy a new drive, and if so what one?
The Dell Precision 390 is from the 2006 and according to the specs the CD/DVD drive was an optional device. You could google the drive and verify its read/write capabilities.
If it does not support DVD-DL (double Layer) then, as pdxales, suggested For $18 bucks as you need to replacing drive.
If the drive is 5 years old it could also be defective, Simple test would be to put a DVD that is double layer into it (ie a DVD movie, any dvd with more than 4.7 gigs) and see if you can "explore" (ie list all the files). Also you can buy a cheap DVD-DL R disk (about $1.00 per disk) and see if you can read / write to the disk.