My iPhone 4 lost power

My Iphone 4 had been charging while battery level was 50%, then about 1 hour later I came back it was totally turned off. I tried many ways but can't turn it on. When I connected to Itunes, It showed a message that: "Itunes has detected an iphone in recovery mode, you have to restore..."

When I connected to redn0w, It informed " Soft DFU mode"

I tried to restore my iPhone to Ios7 then got error 4014.

I haven't jailbreak my Iphone yet.

So do you guys know what is my Iphone's problem?

Is it just software, or battery or power ic?

Please Help!

via iLounge Forums http://forums.ilounge.com/iphone/278769-my-iphone-4-lost-power.html