Well, I found another possibility. When I reprogrammed my flexkey on the mainboard, I noticed that it can also be turned into an on/off button for the lighting. The corresponding information can be found under 1.6 in the user manual. I tried it out for fun and it worked perfectly. Hope it helps you ;)

(Of course, if you are working with a costum water cooling system, the key may be hard to reach).

I don't know your exact settings, but there are basically two possible solutions. One is via Armory crate: Go to AuraSync, then to AURAEffects. There you will find the setting "dark", which switches off the LEDs. You can do this before switching off the PC and the problem should be solved. Variant two is guaranteed to work. Simply switch off the power supply to the powersupply after shutting down the PC. This will cause nothing to light up in the PC. Kind regards :)