Update your post to include full system hardware specs and OS information.
Include PSU: make, model, wattage, age, condition (original to build, new, refurbished, used)? History of heavy gaming use? Or video editing?
Disk drive(s): make, model, capacity, how full?
Look in Reliability History and Event Viewer for any error codes, warnings, or even informational events just before or at the times of the "turn offs".
Overall if you see a history of increasing numbers of errors and varying errors then the PSU is a potential suspect.
More information needed.