I was planning on buying one of those lens cleaners discs here soon and then see what happens.
That might do. There is the 'poor man's' alternative. Take a fine microfiber cloth (eyeglasses cleaning cloth) and wrap it around a business card. Insert it gently into the slot. Some times it works. Do not dismiss the possibility that the DVD drive is kaput.
I did purchase this laptop from my brother a couple years ago. He told me the first operating system that was on the laptop was OS X 10.6. He gave me the disc to install,
According to the information that I have, a Mid 2009 MBP came with Leopard (10.5). You will have to install Leopard (if you have the original disk) or purchase from the online store a Snow Leopard (10.6.3) retail disk.
This disk is a requisite in order to install and run Lion (10.7) or any other newer OSX. You have to update Snow Leopard to 10.6.8 before downloading and installing Lion.