I'd start with booting from a Linux disc or stick (free to make, if you don't have one) and then looking at and testing the hard disk.
That might show if it suffices to replace the hard disk and restore your latest image backup, or that you need to replace the motherboard.
So I have a lenovo ideapad 300. Ons time it lagged and i restarted it. When i opened it it said"noo bootable device or--insert boot disk or try again. How do i fix this?