Why do I get a grey screen and a loading bar every time I open my laptop?

For the past 2 days, every time I've opened my laptop after a few hours or so my laptop would make a whirring noise, turn translucent grey, and have a loading bar. Then when the bar was fully loaded, the screen was back to normal, but I'd have to wait a few seconds to type in my password or move the mouse. I've only had this laptop for about 3 months now. What's going on?