My system seems to crash from time to time. I still don't know what causes it.

If I leave it untouched for a few hours, sometimes, it crashes.

To resume, I have to force a reboot by unplugging the power cable (not even pressing the power button for N seconds seems to work).

Then, it seems to work just fine (after displaying some error messages about lost or orphaned inodes at boot). Until, one day, it happens again. When? I never know. It seems to follow some strange and unpredictable pattern.

Where should I start investigating?