I had this happen about 3 months ago. So changed my power supply and bought another one. But again, the same problem started reappearing. The CPU temperature is fine. I tried changing PSU cables, sockets, ram, graphics cards and cleaned the entire PC, but no avail.
Specs
Motherboard: Gigabyte H61M S2PV
Power supply: Corsair CX550(bought 3 months ago)
Processor: I3 3220
GPU: Sapphire R7 265
Fan: Intel stock fan
Specs
Motherboard: Gigabyte H61M S2PV
Power supply: Corsair CX550(bought 3 months ago)
Processor: I3 3220
GPU: Sapphire R7 265
Fan: Intel stock fan