There are no Moon/Sun/Stars at the sky.

Ah... The sky is blue.. And the cloud is fluffy...
Wait a minutes, where's the sun??
Ah... It's night time now.. The stars should be twinkling...
Oh something's wrong. Why my sky doesn't have moon and stars?? O.o

Please fix asap!
(I'm gonnas say my computer is not too good...)

Specs (Manual Crash) / Settings:
http://pastebin.com/rQ0TCw5u