My iPhone 4 has a black screen!! Will not do anything.

I have an iPhone 4. IT IS NOT JAILBROKEN

I was using my phone normally...the screen locked as usual, then I wanted to take a picture & when I went to slide the unlock bar, the screen went black.

*****not "lit black" like the screen is powered on... but like it is dead*****

*My phone had a 17% charge on it so I just thought that it died... so I charged it into the wall for about 10 mins..while it weas still charging I pressed the home screen and nothing.

I let it charge a bit longer, uninteruppted for about 20 mins... usually the battery screen is displayed after that amount of charging.
Nothing.

I have tried all of the combinations Ive found on this website as well as youtube and google.

- Hold top key 5 secs+home key 10..let go of top button and continued to hold home key.
-"" plug into the computer for a restore window to open.
Nothing.

AGAIN... NOT JAILBROKEN.

I recently backed up my phone to my computer bc iCloud was messing up my phone.
It restored and was working perfectly, then about 2 hours it this happened...

HELP!!

Thank you!