Why does my system fail to boot Defense Grid?

Starting Defense Grid was a nightmare; the ASUS PRIME B660M-K D4 wouldn't boot. I swapped RAM slots, which caused a BSOD. I used GamePP BIOS Wizard to switch XMP to Profile 2 and set voltage to 1.40V. MemTest86 confirmed 100% boot success. AIDA64 showed 45-50°C. HWiNFO verified 1.40V. Stability is achieved.