Python Pygame Zero: Stuck on Not responding

Question

so I was programming with Python, specifically Pygame. I came across a few problems, which I have fixed. But my latest problem, is that when I ran the game, the window is only black. when

My code so far is this:

import pgzrun


#import pgzero
from pgzero.builtins import Actor, animate, keyboard
import random as r


# settings
TITLE = "Tonk Game"
WIDTH = 800
HEIGHT = 600

enemyAmount = 5
wallpercent= 50

# actors
tank = Actor('tank_green.png')
tank.angle = 90

# variables
bulletH = 0

# bullets
bullets = []

# game  variables
gameWin = False
gameLose = False
gameStart = False

# walls + enemy tank

walls = []

enemies = []
for i in range(enemyAmount):
    enemy = Actor('tank_red.png')
    enemy.x = i*200-10
    enemy.y = 25
    enemy.angle = 270
    enemy.move_count = 0
    enemies.append(enemy)

# explosion particle
explosion = Actor('explosion.png')
explosion.pos = 900, 700

for x in range(16):
    for y in range(10):
        if r.randint(0, 100) < wallpercent:
            wall = Actor('wall.jpeg')

            wall.x = x*50+25
            wall.y = y*50+25+50

            walls.append(wall)


# actors pos
tank.pos = 400, 575

# enemy bullets
enBullets = []

#buttons for main menu (settings)

#these are the button for enemy amount adjustment
diff1= Actor('tank_red.png')
diff2= Actor('tank_red.png')
diff3= Actor('tank_red.png')

diff1.pos=200,400
diff2.pos=400,400
diff3.pos=600,400

diff1.angle=270
diff2.angle=270
diff3.angle=270

#now for wall amount
wol1= Actor('wall.jpeg')
wol2= Actor('wall.jpeg')
wol3= Actor('wall.jpeg')

wol1.pos=200,200
wol2.pos=400,200
wol3.pos=600,200



#this is for the start button
start= Actor('bowl.png')
start.pos= 400,560
start.angle=180

# draw def
def draw():

    screen.clear()

    # these only happen when the game has started
    if gameStart:
        screen.blit('grass.png', (0, 0))

        for wall in walls:
            wall.draw()

        tank.draw()

        explosion.draw()

        for enemy in enemies:
            enemy.draw()

        for bullet in bullets:
            bullet.draw()

        for enBullet in enBullets:
            enBullet.draw()

        screen.draw.text("Enemies remaining: " +str(len(enemies)), topleft=(10, 10))
        if gameWin:
            screen.fill('black')
            screen.draw.text("You Win!", fontsize=80, topleft=(280, 250))
        elif gameLose:
            screen.fill('black')
            screen.draw.text("You Lose!", fontsize=80, topleft=(280, 250))

    while gameStart!= True:
        screen.fill('black')
        #settings title
        screen.draw.text("Settings",topleft=(370, 50))

        #for the enemy amount
        diff1.draw()
        diff2.draw()
        diff3.draw()

        screen.draw.text("3 Enemies",topleft=(160, 360))
        screen.draw.text("5 Enemies",topleft=(360, 360))
        screen.draw.text("8 Enemies",topleft=(560, 360))

        #wall amount
        wol1.draw()
        wol2.draw()
        wol3.draw()

        screen.draw.text("25%",topleft=(185, 190))
        screen.draw.text("50%",topleft=(385, 190))
        screen.draw.text("75%",topleft=(585, 190))
        #start button
        start.draw()

        screen.draw.text("Start",topleft=(382, 555))

def on_mouse_down(pos):
    global enemyAmount
    global wallpercent

    #enemy amount setting
    if diff1.collidepoint(pos):
        enemyAmount= 3
        print(enemyAmount)
    elif diff2.collidepoint(pos):
        enemyAmount= 5
        print(enemyAmount)
    elif diff3.collidepoint(pos):
        enemyAmount= 8
        print(enemyAmount)

    #wall amount setting
    if wol1.collidepoint(pos):
        wallpercent= 75
        print(wallpercent)
    elif wol2.collidepoint(pos):
        wallpercent= 50
        print(wallpercent)
    elif wol3.collidepoint(pos):
        wallpercent=25
        print(wallpercent)

    #start button
    if start.collidepoint(pos):
        startGame= True

# update
def update():
    global bullet
    global tank
    global bulletH
    global enemy
    global gameWin
    global gameLose
    global enemyAmount

    # save original pos tank and enemy tank

    orix = tank.x
    oriy = tank.y

    orinemx = enemy.x
    orinemy = enemy.y

    # thes ehappen on game start

    while gameStart:

        # arrow keys/wasd movement
        if keyboard.right or keyboard.d:
            tank.x = tank.x + 7
            tank.angle = 0
        elif keyboard.left or keyboard.a:
            tank.x = tank.x - 7
            tank.angle = 180
        elif keyboard.up or keyboard.w:
            tank.y = tank.y - 7
            tank.angle = 90
        elif keyboard.down or keyboard.s:
            tank.y = tank.y + 7
            tank.angle = 270

        # tank (and enemy tank) go to original pos
        if tank.collidelist(walls) != -1:
            tank.pos = orix, oriy

        # stop tanks from going outside
        if tank.x > 800 or tank.x < 0 or tank.y > 600 or tank.y < 0:
            tank.x = orix
            tank.y = oriy

        if bulletH == 0:
            # bullet code
            if keyboard.space:
                bullet = Actor('bulletblue.png')
                bullet.angle = tank.angle
                bullet.x = tank.x
                bullet.y = tank.y
                bullets.append(bullet)
                bulletH = 100
        else:
            bulletH -= 1

        # bullet.angle=tank.angle
        # move bullet
        for bullet in bullets:
            if bullet.angle == 0:
                bullet.x += 9
            elif bullet.angle == 180:
                bullet.x -= 9
            elif bullet.angle == 90:
                bullet.y -= 9
            elif bullet.angle == 270:
                bullet.y += 9

        # destroy walls
        for bullet in bullets:
            wallInd = bullet.collidelist(walls)
            if wallInd != -1:
                del walls[wallInd]
                bullets.remove(bullet)
            enInd = bullet.collidelist(enemies)
            if enInd != -1:
                explosion.pos = enemies[enInd].x, enemies[enInd].y
                del enemies[enInd]
                bullets.remove(bullet)
                print("1 Enemy has died. Enemy remaining:"+str(enemyAmount))
                enemyAmount -= 1

        # player dies if hit with enemy bullet

        # enemy bullet destroying walls
        for enBullet in enBullets:
            wallInd = enBullet.collidelist(walls)
            if wallInd != -1:
                del walls[wallInd]
                enBullets.remove(enBullet)

        # enemy movement
        for enemy in enemies:
            choice = r.randint(0, 2)
            if enemy.move_count > 0:
                orinemx = enemy.x
                orinemy = enemy.y
                enemy.move_count -= 1
                if enemy.angle == 0:
                    enemy.x += 9
                elif enemy.angle == 180:
                    enemy.x -= 9
                elif enemy.angle == 90:
                    enemy.y -= 9
                elif enemy.angle == 270:
                    enemy.y += 9
                if enemy.x > 800 or enemy.x < 0 or enemy.y > 600 or enemy.y < 0:
                    enemy.x = orinemx
                    enemy.y = orinemy
                elif enemy.collidelist(walls) != -1:
                    enemy.pos = orinemx, orinemy

            elif choice == 0:
                enemy.move_count = 20

                print("move")
            elif choice == 1:
                enemy.angle = r.randint(0, 3)*90

                print("turn", enemy.angle)
            else:
                enBullet = Actor('bulletred.png')
                enBullet.angle = enemy.angle
                enBullet.x = enemy.x
                enBullet.y = enemy.y
                enBullets.append(enBullet)

                print("shoot")

        for enBullet in enBullets:
            if enBullet.angle == 0:
                enBullet.x += 12
            elif enBullet.angle == 180:
                enBullet.x -= 12
            elif enBullet.angle == 90:
                enBullet.y -= 12
            elif enBullet.angle == 270:
                enBullet.y += 12
            if enBullet.colliderect(tank):
                gameLose = True

        # turn on and off the gameWin variable
        if enemyAmount == 0:
            gameWin = True
    
pgzrun.go()

I have tried looking everywhere else, but nothing seems to be working. All the solutions I found are only applicable to a Pygame, whilst I am using Pygame Zero.