If you have properly mounted your hard drive (if on Linux, using static mount via /etc/fstab), then your Node should start up again automatically after your machine has rebooted.
However, power failures on machines not protected by a UPS or other abrupt disconnections may cause database corruption (you would find,
database error: database disk image is malformed in your logs).
Incorrect mounting could lead the Node to not recognize the proper data location where the Node was previously storing the data, resulting in new data getting stored in the wrong directory and the node being unable to find previously stored files when queried.
Such failures should be attended to immediately as they can lead to the node getting disqualified. Here are instructions on how to fix a malformed database disk image. If you need assistance, please ask on our forum.