My phone is acting weird?

HTC EVO design 4g, I've had it for a little over a year now and for the past week it will not stay on. Sometimes it works with the charger sometimes it doesn't. Sometimes it'll stay on for an hour, sometimes it will turn off right when it starts up. I'm really frustrated since this is my first nice phone. I've dropped it a few times but it has no water damage and is still in almost perfect shape. I took it to my sprint tech support and all they did was reset it, which I had already done twice. They also told me if the problem persists I have to pay $100 friggin bucks to replace it.

I'm really trying to get around having to buy a new one I don't have $100 to spend on myself.

If you have any info or have had this problem and know a solution please help me! Thanks