From some googling this seems to be a common issue with the XP3 8300 series of desktops. Whenever I put in any memory card it would show up under “My Computer” but when I clicked on it, I got the “please insert media to drive x”. I could get it to see it if I rebooted the machine with the card in it, but this is not practical for my uses. From what I read on the Dell forums they were just sending out techs to replace the mother boards, as must as I enjoy the reader I would sooner buy a new one then spend the hours on the phone with India and go through to inconvenience of getting a motherboard replacement.
So onto the fix, first thing I did was download the updated driver here (this gives cool new icons that represent the different memory cards so its easier to navigate)
Once you have the driver installed, insert your memory card and it will popup under “My Computer”, right click on it and hit “eject”. I got an error message with the options to “ignore” , “cancel” or “continue” – hit continue and once your card is successfully ejected, put it right back in. Then you should get the windows pop up that asks how to open the media and your card will now be accessible. Once you do the eject and re-plug method once you will be able to pull it out and put it back in without having the manually eject. Hope this helps someone avoid dealing with Dell customer support.