Samsung S4 mini - Android is optimizing app

I have Galaxy S4 mini and it showed a message that the Android is optimizing apps, then it hanged at second app, later the phone is not able to boot/Start. Nothing gets displayed on the screen, it just shows a blank black screen. I tried the Volume up + Power + Home button but nothing happened except that the phone vibrated. I need to reset the phone, how do I do it? I think the cache/RAM is overloaded.