After I pressed the power button. It would only post if I pressed any key on the keyboard. The one facing up (the flat one), is the positive one.
Specs:
CPU: A6-9500 using the stock cooler and the Integrated GPU
MOBO: MSI A320 PRO VD/S
RAM: Kingmax 4GB DDR4-2133
PSU: A generic 600W PSU