I see the problem. The connections to the first 2 buttons are correct. You're missing a yellow wire linking the output of the bottom 2 buttons to AO however, so the 3rd and 4th buttons are not connected to your A0 pin at all. Add a yellow wire between row 24 and row 20 on your breadboard.
I see now that there is a green wire connecting rows 24 and 20 together. However, that is the likely place where things go wrong. I would suggest taking a couple of jumpers and connecting them to a multimeter set to continuity mode. Put one in row 28, and then test continuity to row 24, row 20, and row 16.
One of your wires may not be seated into the breadboard properly, or you may even have a bad row on your breadboard. I've seen that before.
A multimeter is your friend. If you don't have one, you should get one, and learn how to use it. It's invaluable for troubleshooting circuits. (Get one that has a continuity mode that beeps when it detects continuity, and that has auto-ranging voltage and resistance measurements.)