MacPro with LG Slim Portable DVD Writer

I can read disks that are placed in the LG Slim Portable DVD Writer. But when I put a blank DVD into the writer my computer refuses to acknowledge the writer. I can't access the writer so I can't burn anything onto the blank DVD. I started with an "old" LG writer and bought a brand new one, same response. I had been using a "hub" and switched to the adapter recommended by Best Buy, same response. I have read the user manual which doesn't help. The "exe" files on the disk supplied with the writer do not do anything. I swear this was "plug and play" two years ago on the same computer, what happened?!?