Android 4.4 KitKat的模拟器还没有开始。

I am creating an emulator for Android 4.4 KitKat, but the emulator takes very long and isn't starting. I tried many devices like Nexus4, Galaxy Nexus, Nexus S etc. but none of that worked. Just a black screen with the android logo for long time. Any suggestions?I am creating an emulator for Android 4.4 KitKa