@aromarood - I had the same issue and was able to resolve it myself after a wasted trip to the “genius” bar to be told by a moron that I could buy a wireless keyboard.
It is important that the space bar is both removed and replaced in the right manner to avoid breaking delicate plastic clips on the underside of the key and because one set of clips is designed to slide into the scissor mechanisms while the other side clips down vertically after you have engaged the other set of clips by sliding them in horizontally. It is much easier to demonstrate than to explain.
In my first attempt I forgot to remove the lengths of wire from the underside of the key before replacing the key. When you pry the key off they tend to stay with the key, but you must set them in their correct positions on the base plate before you press the key back on or the key will not spring up when depressed - which sounds like the situation you have.
In the image below you can see the wires still attached to the key. They are retained by small plastic clips. You can gently free them from the key using your fingernail.
To replace the key they need to be placed in the same orientation on the base plate with the short hooks under the metal hooks on the base plate at either end of the space bar recess. Be very careful not to bend or break the small metal hooks on the base plate or you will be up for a whole upper shell replacement.
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