Wrestle around the little metal bar under the key. As you can see, it fits in little slots on the keyboard, and little slots on he key itself. Press the metal bar onto the slots on the keyboard. Align it so that when you push in the space key, the bar will also pop into the slots on the key. Then put in the key, still making sure everything aligns perfectly. Next, using all your force, SLAM your fist into the key, pushing it in, hopefully making the key both snap on the plastic parts on the keyboard, and the metal bar.
There are probably similar bars under the left shift and numpad 0 keys. Watch out.
Also, why ask on GTM?