The cover slides about 1/4 to 1/2 inch towards the front of the computer to clear the slots. Press down lightly to slide it. Make sure you have the correct side facing up--it is easy to make the mistake of having the computer turned the wrong way. Study the photo here: <ADMIN NOTE: Broken link has been removed from this post by Dell>
Thanks Mary. Yes that's the same manual I'm using. I'm applying as much pressure in a forward direction as I can without breaking something, but it seems to be catching on something. It looks like it only moves about 1/16 of an inch and then it gets stopped by the edges of the front bezel. Does the front face need to come off first? I never had a computer so hard to open like this. I appreciate your advice. If you have any more ideas I'm pretty much stumped.
I finally got the cover off. I should note that the front bezel comes off with the cover. It was on there pretty tight but I kept at it and finally it came off. I was able to install a Crucial 64GB SSD. The Optiplex FX160 bakes a nice little home computer when you installa hard drive. I think I may add some more memory. But for the price at the outlet store its a nice little machine.
It seems the Dell manual misses out many 'obvious' steps to move the cover, let me help: