I am using iphone 4s 8 gb. when i was in some apps and try to come out from it i could not and when i lock it and try to unlock there is no display also try to call from unother phone to my iphone will ring but there is no display.

Hello pgns,

I understand that your iPhone's display has suddenly gone dark on you. Fortunately the steps outlined below can help restore functionality to your iPhone.

1. Plug in your device to a power source. If you see the low-battery screen when you plug in, let your device charge for at least 10 minutes (20 minutes for iPad) before using it.
2. Force restart your device while it's plugged in.
3. If this doesn't work, restore your device.
4. If you still see the issue after you restore, contact Apple Support.

Get help with the screen on your iPhone, iPad, or iPod touch
https://support.apple.com/en-us/HT203039

Sincerely

Hello

I understand the problem you have faced it happened on my iPhone 6s too

to recover your iPhone just press power button + home button together till it restarts .