My Lenovo Laptop is stuck on the start-up

Hello,
I was working on my laptop when it slowed down. After a few lags a prompt message appeared that windows is not responding. I clicked on the end session and switched it off. When I tried to turn it back on it is stuck on the start up screen with the "lenovo" brand name. There's a loading icon on the bottom but that's it. It stays on like that for more than 30minutes now.What should I do?Please help.