Why does my laptop sometime say operating system not found?

My laptop is on all the time and the charger plugged in. Does that have something to do with this message? I have a Sony Vaio with Vista.

When I open my laptop, it will display a black screen with “operating system not found.”

But I can turn it off then on again and it will boot up just fine. I can access everything from my desktop and get online so I’m kind of confused why I get this message.
I’m thinking I need a new a laptop, it’s been with me for about five years.