Simply put, DVD-R, DVD+R, and the like are different DVD formats. Think of it as the PAL, Secam, and NTSC of DVDs
. If that doesn't ring any bells, either, then never mind. It's no big deal anyway.
As to your problem, unfortunately I don't think I can be of much help, since I still don't have enough information. So my best advice to you is, wait a couple of days, maybe someone in here knows what to do and will tell you about a solution. If nobody answers, then maybe you should just get your DVD to a repair shop. I don't think it'd cost too much, since I don't believe it's a big problem in the first place, and secondly because DVDs have become so cheap these days, so how expensive could fixing one get??!!
Good luck, man.