Sorry for the late response.
Thank you very much for your replies.
I tried everything, but couldn't solve it. And there's no option to adjust memory controller voltage in the advanced settings; only memory voltage. Guess it's not adjustable for the chipset.
Rexer: Thank you for your reply. Yes, I have a UPS. Meanwhile, I also checked with a 650W PSU. Same problem.
Thanks again, everyone, for your time and help.