It could be the electricity supplier of your area decreasing the voltage or the power. In that case you can't do much. Many companies do that during night time.
It could also be the circuit breaker that manages electrical flow on the room being faulty. In that case you could just connect the PC to another plug to find out (make sure that the other plug does not share the same circuit breaker as the current plug. In short, connect the PC to a different room on the other side of the house or something).
It could also be the circuit breaker that manages electrical flow on the room being faulty. In that case you could just connect the PC to another plug to find out (make sure that the other plug does not share the same circuit breaker as the current plug. In short, connect the PC to a different room on the other side of the house or something).