Why is my iphone keep restarting itself??!!!

Ive had my iphone for a long time now, and its been having very big problems latley. Its not in service, i just use it for music. Im pretty sure its the first iphone, and one day, none of the downloaded apps worked, unless it was the apps that came with it, like safari, youtube ect.. so i erased all the settings on the phone so i could restart it, so that the apps could work again, but after i did that it kept restarting itself, OVER, and OVER again. it did this for about 2 days. then it died, and i plugged it in and now its just sits there on the startup screen like its going to turn on, but it doesnt, it just sits ther and restarts itself, over and over and ver and over. and its been doing this for sometime now. i really want my ipod back. nothing is working. i am extremley frustrated. please help me.