My cell is acting up, it won't stay on for me.?

I have a Samsung (Flip phone) and I use at&t. a day or two ago it did this black phone with a red dash through it which means I can't send a txt or call. Well yesterday it does this thing of turning off over and over without the turn on chime, Its fully charged and I am sure it is. We took out the battery and left it and then it just turns on over and over. Today it jus turns on and off randomly, not allowing me to even access my phone. What is going on? Oh, and sorry if I posted this in the wrong category, I couldn't find anything specifically on phones