The mounting tabs on the control panel frame have cracked off most likely due to age, heat, or imperfections in the plastic.
If the tape idea doesn't appeal to you (*grin*) it will need a new control panel frame. That normally comes with a new keypad, but I would need the model number to be sure.
It is probably going to be referred to as the control panel in the parts list and it should run about $50 plus shipping.
You can find helpful exploded view diagrams and order parts by entering your full model number here: http://tinyurl.com/gv383
Also, these units have mini-manuals hidden behind the control panel and they're very handy to use.
If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk
Normally you would unplug the oven from the wall, remove the 2 or 3 screws holding the grille in place, remove the screw at the top of the control panel frame, then CAREFULLY lift up and out to remove it.
Then you can mark and/or photograph the wires to be sure they all get back in the same place. Then you can see how the circuit board would come out and then go into the new control panel frame.
If you don't want to replace it, I would suggest that you get it squeaky clean and dry and use a small amount of household cement or Elmer's Glue-All (not super glue) on just the bottom edge, then temporarily use tape to hold it firmly in place until it has cured and dried.
Please write back with more details if you need further help.
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