What could have been the mistake?

Today my working laptop had just thought no I delete Windows 10 …, someone else brought everything back to normal (I'm very grateful) and it started in such a way that he didn't want to open anything… So absolutely nothing and then I wanted to restart quickly completely stuck, pressed the main button and then turned on normally did not try it several times. What could be the mistake? (Laptop is a simple thinkpad 520)

BIOS problem?

With such spontaneous failures, I always remember the hard drive. If any sectors have a bang, the whole system can be damaged. But you will notice that in the future when he starts spinning around again.

It would still be good to know how the person got Windows 10 up and running again.

Backup the data to other hard drives. And then redesigned it

After all, very positive that there was a backup. Then the error can occur again and again if the hard disk should have any problems. Strangely, I also have certain problems with old hdds that have been running for eight years, where tests never reveal any errors, but the system crashes when there's greater access to these disks.