My iPhone 4s camera won't work?

Everytime I go onto my camera it's just black and nothing happens even when you try and switch from front to back camera! When I go onto camera it makes my whole phone freeze for a few seconds, especially when on snapchat! I'm going on holiday in 2 days so can someone please help me fix this as I will want to take pictures.

Ps. My phone screen has been replaced several times due to me dropping it and it smashing if that is the problem? And it's currently smashed and there's no glass over the front camera but the front camera is still there and works 1/100 times, same with the back!
I just want my phone back to normal please

You dropping it may be the issue why it won't work now

I'm very sorry to say that your phone has been possessed by the stoptheselfies gang. These group of individuals do not tolerate any self absorbed people, any attention seekers, or anyone who is taking selfies instead of making the world a better place. The way to fix your problem is to travel to a third world country, take a photo of a poor family, and I don't mean take a selfie with them just a pic of them, and then give them your phone. The family will be so grateful and shower you with many blessings, and the stoptheselfies gang will leave you alone.

Close the camera app by double tapping the home button and after that open it back up. Hopefully this helps… My screen isn't cracked so i don't know