What cause lag (Pygame Main menu)?

Question

I'm currently programming a game using Pygame, once I implemented the Main Menu, the FPS of my game were divided by two, What could possibly cause that lag? (I'm talking about the framerate while playing, when the Main menu is not visible)

There is the code for the Main Menu (point list is the list of point for the polygon to display the current selection):

import sys,os
import pygame
from Hud_implem import *
class MainMenu(object):
    def main(self,screen):
        self.buttonlist = [[0]]
        self.buttonlist.append(self.pointlist((58.104,32.148),(69.396,23.915),(69.369,30.296),(58.104,38.630)))
        self.buttonlist.append(self.pointlist((58.104,41.407),(77.229,27.296),(77.229,33.777),(58.104,47.888)))
        self.buttonlist.append(self.pointlist((58.104,50.037),(74.187,38.185),(74.189,44.666),(58.104,56.519)))
        self.buttonlist.append(self.pointlist((58.104,58.704),(66.396,52.593),(66.396,59.074),(58.104,65.185)))
        clock = pygame.time.Clock()
        screen_image = pygame.image.load(os.path.join("Images","Title Screen.png")).convert_alpha()
        screen_image.set_colorkey((193,56,57))
        screen_image = pygame.transform.smoothscale(screen_image,(SCREEN_W,SCREEN_H))
        selection_layer = pygame.Surface((SCREEN_W,SCREEN_H))
        selection_layer.fill((255,255,255))
        selection_layer.set_colorkey((255,255,255))
        selection_layer.set_alpha(100)
        self.selectioned = 1
        self.movecountdown = 0
        while  not started:
            dt = clock.tick(60)
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    return
                if event.type == pygame.KEYDOWN and event.key == 13:
                    self.get_pressed()
            screen.fill((49,103,124),((0,0),screen.get_size()))
            self.get_selection(selection_layer,screen,dt/1000.)
            screen.blit(screen_image,(0,0))
            pygame.display.flip()

    def get_pressed(self):
        if self.selectioned == 1 or self.selectioned == 2:
            #started = True
            Game().main(screen)
        elif self.selectioned == 4:
            pygame.quit()
    def get_selection(self,layer,screen,dt):
        keys_pressed = pygame.key.get_pressed()
        if keys_pressed[pygame.K_UP] and not self.movecountdown:
            self.selectioned += -1
            self.movecountdown = 0.2 #NOT 2 DISPLACEMENT AT A TIME
        if keys_pressed[pygame.K_DOWN] and not self.movecountdown:
            self.selectioned += 1
            self.movecountdown = 0.2 #NOT 2 DISPLACEMENT AT A TIME

        if self.selectioned > 4:
            self.selectioned = 1
        if self.selectioned < 1:
            self.selectioned = 4
        self.movecountdown -= dt
        if self.movecountdown < 0:
            self.movecountdown = 0
        layer.fill((255,255,255))
        pygame.draw.polygon(layer,(0,0,0),self.buttonlist[self.selectioned])
        screen.blit(layer,(0,0))


    def percent(self,percx,percy):
        return (float(percx/100*SCREEN_W),float(percy/100*SCREEN_H))
    def pointlist(self,topleft,topright,bottomright,bottomleft):
        topleft = self.percent(topleft[0],topleft[1])
        topright = self.percent(topright[0],topright[1])
        bottomright = self.percent(bottomright[0],bottomright[1])
        bottomleft = self.percent(bottomleft[0],bottomleft[1])
        return [topleft,topright,bottomright,bottomleft]


if __name__ == '__main__':
    global started
    started = False
    pygame.init()
    pygame.display.set_caption("Project Swordman","Icon.png")
    pygame.display.set_icon(pygame.image.load(os.path.join("Images","Icon.png")))
    SCREEN_W,SCREEN_H = 1366,768

    #screen = pygame.display.set_mode((SCREEN_W, SCREEN_H),pygame.FULLSCREEN)
    screen = pygame.display.set_mode((SCREEN_W, SCREEN_H))
    MainMenu().main(screen)