random"reboot" procedure without rebooting?

[PhotoRepair]

My i5 3470 rig randomly goes through the reboot procedure without rebooting. The "Boot sound" beep sounds and the fans all whir up to 100% fora few seconds and it all settles down. It does not affect me in any way but it is troubling why it is doing this. I dont do much other than photoshop. At best i'll have chrome open with 4 or 5 tabs, photoshop and nothing else. Chrystal Disk says all my discs are fine, what could be happening? Any clues or help would be most welcome. 

 

Windows 10

650 Watt PSU

32GB Ram

Stock cooler (no over clock)

Gigabyte z77 D3H Mobo

Edited August 22, 2019 by PhotoRepair
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[PhotoRepair]

anyone any ideas?

 

[Jeans]

Have you checked temps while running your usual stuff? When was the last time you redid the thermal paste (Since it is a 3rd gen i5)?

Not sure about new ones, but on old cpu's there was a sort of fail-safe when it gets too hot in that it force a reboot.