Jailbroken iphone wont respond to anything?

Ok so i jailbroke my iphone 3gs with green poison, ios 4.2.1 After like 2 weeks it turned off automatically. i tried pressing home and power at the same time, the light went white and then it went black. right now it just a dim blue light, itunes wont recognize it and it wont turn on or show the apple logo. the phone is like a month old with no water or physical damage. it wont go into dfu or recovery mode. i just want to restore it and take it to apple because i still have warranty on it. please help, and also i beleive it is an unthethered jailbreak, because i have turned it off and on before..