You have provided us with almost no information so we can't help you.
When you turn the laptop on it restarts? How far in the boot process does it get? Does it get to the same spot every time? Is it plugged in or running on battery? Can you boot in safe mode? What are the specs of the laptop? What version of Windows is it running?
This is one of my biggest pet peeves. This is a forum, not Google. All of us will be happy to help you, just please provide as much information as you possibly can.
Building on what jmacavali said, exactly what happens when you press the power button?
But seriously we have nothing to work off of to help you. You need to be much more specific in the issue you are having. give us everything that jmacavali asked for then we can help.