My DVD-RW Drive is Having Problems!!!

I have little idea what the problem is here. I have two drives on my computer. Both have been add-ons: a DVD R/RW drive and a DVD ROM drive that can read DVDs but not burn them. I used to be able to burn data DVDs using Nero Express, and my DVD Rom drive could read them without a problem. For some reason, I can't anymore. When I burn the discs full of mpg & avi files, Nero says that the burn was completed successfully. Results vary when I put the disc in my second drive. When I open the disc, everything looks fine, and the files seem to be on the disc, but I have poorer luck when I actually click on a file name. Either I can play some tracks but not all of them, or the discs are wholly faulty. When I try to play some of the mpg data files, it takes forever and eventually tells me that the disc may be damaged or dirty. When I put the discs in other computers, I get the same results. I've tried playing with Nero's settings but no avail. I've also used a variety of virus and adware software removal programs and removed quite a few viruses, adware, and spybots. Where can I go from here?

The DVD R/RW drive, by the way, has never been able to play data DVDs (it says something like "I/O redundancy error" when I try), but I hadn't had any problems playing them on the DVD ROM drive before. In fact, I can burn DVDs to play in my regular DVD player just fine. Please help me!