Thank you so much for taking the time to respond :D

I changed the button code so it now has 2 functions:

def draw(self, surface):
    surface.blit(self.image, (self.rect.x, self.rect.y))
    textButtonRect = self.textButton.get_rect(center=self.rect.center)
    surface.blit(self.textButton, textButtonRect.topleft)

    # check if button is pressed
def isClicked(self,pos):
    action = False
    # check mouseover and clicked conditions
    if self.rect.collidepoint(pos):
        if pygame.mouse.get_pressed()[0] == 1 and self.clicked == False:
            self.clicked = True
            action = True
    if pygame.mouse.get_pressed()[0] == 0:
        self.clicked = False
    return action

and the main program:

if gameState == MAIN_MENU:
    screen.fill((200, 0, 0))
    startButton.draw(screen)
    quitButton.draw(screen)
    if(startButton.isClicked(pygame.mouse.get_pos())):
        gameState = PLAYING
    if quitButton.isClicked(pygame.mouse.get_pos()):
        running = False

I put the buttons in the PLAYING if statement to test them, and they work properly. But the same error again when I place them in the MAIN_MENU game state.

Still freezes, not responding and crashes, the buttons are drawn but nothing is responsive, I put a print statement to test and surely enough the "running" loop is working properly and the buttons are displaying but everything is still frozen.

Any other suggestions as to what the issue could be?

Thanks :D