Use the Novo button on the left side of the laptop. It's a small pin-hole, and it brings up a very basic menu allowing you to reset the computer.
The repair loop is a very common situation with Windows 10, and there are any number of reasons why and when it occurs, including installing automatic Windows updates.
Once you get your machine back on track, make it a habit to copy important files to an external drive, e.g. OneDrive or uploading them to DropBox or a similar cloud-based option.