ruby フリーズ

この、プログラムを実行すると、いつも、フリーズしてしまいます。
なぜフリーズしてしまうのでしょうか。 エラーメッセージは出ていません。
使っているruby はruby 1.9.3p385です。

このような感じで止まってしまいます。
スコアも表示できませんし、数字を入力しようとすると動かなくなります。
10.times doあたりが、おかしいのだと思いますが、どのように直したらよいかわかりません。クイズを１０問ほどといてスコアを稼いでいくというプログラムを作りたいです。
main.rb

#!ruby -Ks
require "./window.rb"
require "./kuizu.rb"

window = Window.new
window.drawBack
window.gamestart
window.refresh

while true do 
  while event = SDL::Event2.poll do
     case event
       when SDL::Event2::Quit
            exit
       when SDL::Event2::MouseButtonDown
           x = event.x
           y = event.y
           if window.kuizuclicked?(x,y)
              hajime
              window.refresh
           end
           if window.zairyoclicked?(x,y)
             require "./zairyo.rb"
           end
       end
  end

end

widndow.rb

require "sdl"
require "./color.rb"
class Window
 WINDOW_YOKO = 750
 WINDOW_TATE = 550
 BITPIKUSERU = 0
 KUIZUX =      550
 KUIZUY =      200
 ZAIRYOX =    570
 ZAIRYOY =    300 
def initialize
   SDL.init(SDL::INIT_EVERYTHING)
    @screen = SDL.set_video_mode(WINDOW_YOKO,WINDOW_TATE,BITPIKUSERU,SDL::SWSURFACE)
    SDL::TTF.init
    @font = SDL::Kanji.open("font/jiskan24.bdf",24)
    @font.set_coding_system(SDL::Kanji::SJIS)
end

def drawBack
 @screen.fill_rect(0,0,WINDOW_YOKO,WINDOW_TATE,Color::GREEN)
 @font.put(@screen,"###",230,50,255,255,255)
end

def refresh
  @screen.update_rect(0,0,0,0)  
end

def gamestart
 @font.put(@screen,"ああああ",KUIZUX,KUIZUY,255,255,255)
 @font.put(@screen,"いいいい",    ZAIRYOX,ZAIRYOY,255,255,255)
end

def kuizuclicked?(x,y)
  if  (KUIZUX <= x) and (x <= 690) and (KUIZUY <= y) and (y <= 230)  
    return true
  else
    return false
  end
end

def zairyoclicked?(x,y)
  if  (ZAIRYOX <= x) and (x <= 600) and (ZAIRYOY <= y) and (y <= 330)  
    return true
  else
    return false
  end
end

end

kuizu.rb

#!ruby -Ks
require "sdl"
require "./color.rb"
require 'io/console'


$tisiki = open("./dat/score.dat","w")


def yomikomi()
  i = 0
  j = 0
  $moji =[]
  f = open("./dat/mondai1.dat","r")
 while text = f.gets do
    $moji[i] = text.chomp
    i += 1
 end
  f.close
  $mondaisu = i/8
 while j <= i/8
    eval("$q#{j} = [ $moji[j*8+0],$moji[j*8+1],$moji[j*8+2], $moji[j*8+3],$moji[j*8+4],$moji[j*8+5],$moji[j*8+6],$moji[j*8+7 ] ]")
    j += 1
 end
 q = []
 eval("q = $q#{rand($mondaisu)}.clone")
 $mondai     = q[0]
 $sentakusi1 = q[1]
 $sentakusi2 = q[2]
 $sentakusi3 = q[3]
 $sentakusi4 = q[4]
 $sentakusi5 = q[5]
 $kotae      = q[6]
 $score      = q[7]
end



class Gmen
 WINDOW_YOKO = 750
 WINDOW_TATE = 550
 BITPIKUSERU = 0


 def initialize
   SDL.init(SDL::INIT_EVERYTHING)
    @screen2 = SDL.set_video_mode(WINDOW_YOKO,WINDOW_TATE,BITPIKUSERU,SDL::SWSURFACE)
    SDL::TTF.init
    @font = SDL::Kanji.open("font/jiskan24.bdf",24) 
    @font.set_coding_system(SDL::Kanji::SJIS)
    @font2 = SDL::TTF.open("C:/WINDOWS/Fonts/TAHOMA.TTF",30)
 end

 def drawBack
  @screen2.fill_rect(0,0,WINDOW_YOKO,WINDOW_TATE,Color::WHITE)
 end

 def refresh
  @screen2.update_rect(0,0,0,0)  
 end

 def kotaeawase
  a = gets.chomp
  @font.put(@screen2,"入力した数字#{a}",50,280,0,0,0)
 if a == $kotae.to_i
   $tisiki = $tisiki.to_i + $score.to_i
   @font.put(@screen2,"正解です",50,250,0,0,0)
   @font.put(@screen2,"正解は#{$kotae}です。",50,220,0,0,0)
 else
  @font.put(@screen2,"間違いです。",50,250,0,0,0)
  @font.put(@screen2,"正解は#{$kotae}です。",50,220,0,0,0)
 end
 end


 def start
    @font.put(@screen2,"今###異なります。",50,30,0,0,0)
    @font.put(@screen2,"正##解さい。",50,70,0,0,0)
    @font.put(@screen2,"始め##い。",50,120,0,0,0)
    refresh
  while true do
    while event = SDL::Event2.poll 
       case event 
         when SDL::Event2::Quit
            exit
         when SDL::Event2::KeyDown
          if event.sym == SDL::Key::SPACE then
            10.times do
             yomikomi 
             drawBack
             mondaihyouji
             refresh
             kotaeawase
            end
          end
       end
    end 
  end
 end

 def mondaihyouji
  @font.put(@screen2,"#{$mondai}",   50,20,0,0,0)
  @font.put(@screen2,"#{$sentakusi1}", 50,50,0,0,0)
  @font.put(@screen2,"#{$sentakusi2}", 50,80,0,0,0)
  @font.put(@screen2,"#{$sentakusi3}", 50,110,0,0,0)
  @font.put(@screen2,"#{$sentakusi4}", 50,140,0,0,0)
  @font.put(@screen2,"#{$sentakusi5}", 50,170,0,0,0)
  @font2.draw_solid_utf8(@screen2," #{$tisiki}",100,500,0,0,0)
 end
end




def hajime
 g = Gmen.new
 g.drawBack 
 g.refresh
 g.start
end

必要な部分があればコメントください。