How to open Dell Optiplex gx280 case?

Third latch, top right corner in back panel with green plastic tab seems to be keeping case from opening. Cannot figure out how to release this catch. Do I just use a crow bar? Thanks.

Don't know much about this Dell line, I did however have a few GX's come thru last week. No 280's but a couple of 240's.
The latch with the green tab is more than likely the expansion card lock and has nothing to do with opening the case.
There are 2 buttons, 1 on the top and 1 on the bottom ( or left and right depending on wether you use a tower or desktop configuration ) these are all that need to be depressed to open the case.
If you're have problems, try releasing one side then the other, worked for me on these systems.