Welcome!
If pressing on the spacebar helps and the connections look okay, I'm guessing there is some problem inside the keyboard itself (?) and see the 2 options below if nobody has better ideas to fix it.
1. If you're still under warranty, you can send it in for warranty service.
2. If your notebook is out-of-warranty, you can purchase a keyboard from our
eStore site.
I didn't see the G53Sx keyboard posted, but it should use the same keyboard as the G53Sw which you may also want to confirm with eStore or inquire about.