iPhone 4S Camera crashes iPhone

iPhone 4S, iOS 7.1.1

My camera won't work. When I try to open it, the whole phone crashes every time. No matter if I want to use the front or back camera. To add up: Other camera apps wont work either and will crash my iPhone as well. I have the problem since iOS 7.

Weird thing ist, that it sometimes works for a while and then crashes again and the camera won't work for a long period again.

When I charge it, I shouldnt use my phone at all, because it crashes as well and has a lot of trouble to boot in the first place.

I resetted it more than once, setted it up as a new iPhone - no change. It even crashes often without a reason and has problems to boot again..

I own it since 3 years now.

Could it probably be a hardware problem?

Thanks for your answers!