Help! My cell phone won't turn back on. ?

Yesterday I accidentally dropped my phone into the water. I picked it up immediately but it was submerged pretty deep. I took out the battery and dried the back, and later it turned on and was working perfectly. However, when I got home it kept turning on and off randomly. Finally I got it to turn on and stay on. When I woke up this morning however, it was off and would turn back on. I tried charging it but it just sits there and won't turn on. I looked on the Internet and tried removing the battery again for an extended period of time, and also tried holding down the power on for more than five seconds in order to reboot it or something likewise. Neither one worked. Does anyone else have any ideas on what I should do? Or should I just purchase a new battery? If I should get a new battery, would it be easier to go to AT&T or just a store that sells batteries? The phone is a Samsung Flight. Any help would be greatly appreciated. Thank you!