Why won't my IPhone 4 turn on at all?

(My IPhone 4 had been bought on EBay and I have had troubles with it before)

I had being using my IPhone 4 earlier and it was working fine. The battery was on 20% so I knew I needed to charge. My sister wanted me to help her with her homework so I left my phone not charging. After about 10 minutes of helping my sister I came back to get my phone. Once I came back the screen was black and won't turn on. I have left it charging all night and nothing is going on. It makes a messed up noise when my sister tried to call it but that is it, I tried calling it again this morning and nothing happened.

Being a writer I write on my phone on an app. I had not backed it up on I cloud as my phone's I cloud doesn't work. I have about 6 stories with at least 4 pages of writing in each. So I have a horrible feeling its all gone.

Hi please try to connect it to Itunes and put it in recovery mode.(just google this term and you will find a tutorial) :)

If this doesn't work, maybe the cable of the screen isn't connecting well so you think it's off but in reality, the screen is just black/off.