Missing DVD/CD Rom Drives, Registry Values Missing?

Missing my cd/dvd drives. Device manager has them listed but with a yellow exclamation mark. I've tried to delete upper and lower values in registry as reccomended but they are not there. Did a Microsoft guided help and the error says that I'm missing High and Low registry values for my drives. I've done the delete/new hardware scan many times with no success. Where do I find the missing values?
Thanks in advance.