My iphone isnt staying on and not charging.it also says its searching for a signal

Hi, my iphone for some reason has just stopped working. I have no idea what happened to it! My phone would not turn on, even when I plugged it in. So I came back to it 5 days later and plugged it in. It thankfully turned on, but when I unplugged it..it turned off. Wouldn't turn back on. When I plug it in,all it says is that it's searching for a signal. We have a signal here so I don't know why it's saying that. I have tried restarting it MANY times and it isn't working. When I plug it into my laptop, the iphone doesn't come up on Itunes. I'm not sure what to do now. Please can someone help me? Thank you!