Why is my iPhone dieing?

hello, I have a iPhone 4 and it's been dropped quite a bit in its life. just today I put it in my pocket and it shut off. I put it back on a charger after it was charged fully. now I threw it on my bed out of frustration on the face of the phone then it worked again for about 4 hours and now it won't stay on or receive service. I reset, did a hard reset, (home and power button) and it just comes on for a little time maybe 10 minutes and the screen goes white and cuts off. i'm really frustrated with the phone. :(