Hi @eirinik
I would suggest you to open up your laptop and disconnect the hard drive and test again.
I have a feeling your hard drive might be having issues.
Check if you can use F10 for a diagnostic test.
Start from 8 Mins on the provided video link for an idea where your hard drive is located at.
https://www.youtube.com/watch?v=XkZaTGn9_94&vl=en
Should the HDD is faulty, I would suggest you to get SSD for a replacement.