iMac early 2009 both built-in CD drive and external CD drive not working.

Will either drive show normal behavior with commercial DVDs like movies or, in the case of your 2009 iMac, the system install/restore disks that shipped with it? As both an old and a new player do the same thing, consider the media. If you a different brand of disk, try one of those. Not all blank DVDs are creates equally.

This site:

http://www.digitalfaq.com/reviews/dvd-media.htm

has not been recently updated but gives some insight into quality issues among DVD media. Verbatim is normally good but, as that site points out, every company outsources media production to just a handful of manufacturers. Some also have "value lines" that may not be the quality of their flagship products. Interesting site.

You can try resetting the SMC and NVRAM…

Reset NVRAM or PRAM on your Mac - Apple Support

How to reset the System Management Controller (SMC) on your Mac - Apple Support

If neither works you can try the Terminal command from this page.

https://www.wyzant.com/resources/blogs/275369/apple_s_external_superdrive_can_work_on_older_model_macs

It may need cleaning, go to your local office supply store and ask for a CD/DVD cleaning kit and use it. If that fails, then the drive is likely dead. It can be replaced by an external CD/DVD USB drive. OWC (www.macsales.com) has a good selection to choose from based on your needs.