If you press the spacebar at one end, the other end should move down at the same time.
If NOT, then does the spacebar work if you press in the middle of the spacebar?
If this sounds like the problem you're having, then there is a metal bar that transfers downward force across the length of the spacebar that isn't fitted correctly.
Yes, there are tiny plastic clips that can be broken or squashed if not handled correctly, but the above is on of the most common "spacebar" failures that I saw with them.