MacBook keeps shutting down! HELP!

Ok guys, another problem.

If anyone saw, My Keyboard was not working. I went into BestBuy, and they sent it in. A week later. They called me.
I went in about 30 minutes ago. It all works now.
But the NEW problem is that when I start it up, it just automatically shuts down! Whats up with that??
I dont know what the problem is!

PS I also noticed, if you press the power button twice in a row does it make ur sound go up? Cause it does for me!
Help!
Thanks, Luc (shady899)

Edit: It also keeps asking me if I want to shut down...