My camera says battery exhausted when i put new batterys?

I have a usb but i put into the pc the other in the camera but still says it why? Its a nikon L20 cool pix

Did you get a little book when you got your camera? Yes? Read it.No? Get one online and read it. Your batteries are dead, if they are alkalines they are NOT rechargeable. There are very few cameras that charge through USB, I don't think your Nikon is one of them.