DVD/CD drive ejects blank discs. Any suggestions on how to fix it?

My August 2009 15" Macbook Pro's DVD/CD drive is ejecting any blank disc I insert. I'm trying to burn a movie I created in iMovie onto a blank DVD-R and DVD+R. I burned a movie I created about a week ago and it worked then. I tried changing the format of the movie and I tried different DVD types and nothing was working so I figured it's my MBP's optical drive. It ejects blank CDs as well. I wanted to maybe clean the lens myself but I wasn't sure about the correct way to get to the drive with this specific model. Any suggestions? Thanks!