When you flashed the phone (or even if you just do an OTA upgrade) it wipes out both the 'kernel-power' and 'kernel-power settings' packages. Unless both are reinstalled the phone will only load the stock kernel and standard settings. Whatever settings you had before just don't matter, the phone will only run standard settings. So resetting the power settings is not possible or necessary while running the stock kernel. IOW, that's not the cause of the reboots. Maybe the reflash didn't go quite right, maybe you loaded the wrong firmware, maybe your phone has developed a hardware problem, or maybe some software is causing trouble. But trying to fix it by attempting to change power settings while running the stock kernel will get you nowhere.