Recently upgraded Trisquel 8 from 7 fails to boot, any hint?

Hi, this is a notebook from a familiar.

Trisquel 7 worked perfectly in that laptop for more than 5 years.

A couple of weeks ago we did the upgrade to Trisquel 8.

Then the notebook suffered some hangs that demanded hard power-off (the person using the machine doesn't know almost nothing about computers).

And now, at start, system doesn't loads and the display only shows:

---
BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1.4) built-in shell (ash)
Enter 'help for a list of built-in commands.

(initramfs) _
---

Any hint or suggestion?

Maybe I'll have the machine with me starting tomorrow for a couple of days.

Thanks a lot!