|Do you have a UPS to which the PC in question is connected and is the UPS fully functional ? If not, then check how your M/B BIOS is configured as to when there is a power outage and when the power is restored ? |
Go into the BIOS settings and check if you have AC back function under Power Management. It may be SOFT-OFF or FULL-ON or anything for that nature.
Make it SOFT-OFF meaning when there is a power failure, the PC will remain turned off.
When it is FULL-ON, even if your PC is in an off state, it will be on when there is a momentary power cut.
Hope the above helps.