I have just recently had the same exact issue.  I use the Advanced Port Replicator (APR) with my Inspiron 8500 and the CD Drive does not work. Detach it from the docking station (APR) and it works completely.  I am near the end of my 3 year warranty and DELL is fixing it under warranty. 

Dell said it would replace the APR, but after escalating the problem several levels of tech support at DELL, they finally figured out that it is the mother board and not the APR. I am sending my 8500 to them in two days for mother board replacement.  I will find out if this fixes it.  On a parallel path with DELL hardware warranty on-line support, they said they would replace the APR under the computer’s 3 year warranty because I pointed out to them that in the APR manual pg 21 it says that warranty is per the computer documentation.

DELL told me yesterday that they have had the same problem before, at least one instance, but I believe that there are more.  They have discontinued the APR docking station and now have a USB port system.  Apparently the docking port station gets overloaded some how and damages the mother board (Secondary IDE Channel / ComPort) and it only shows up when docked. 

Hope this helps someone. Good luck!!! Do not take NO for an answer from DELL. Escalate to the supervisor level of technical support.  They will finally help you if you are persistent. I like DELL, but sending their tech support off-shore to India ends up making a language barrier and less capability of solving the technical problems.  I really like DELL, have two laptops & a desk top.  I would buy another when it time.

Regards, DELL supporter!

BTW, I handle purchasing for our small company and have purchased at least 25 Dell computers in the past few years (I have four Dells in my office right now.)

I like Dell, but I really hate the way they've been dodging this issue.