RAM boots at the SPD frequency programmed into the DIMM, NOT at the max speed the RAM has been tested to run at stable.
Your system should reboot after you clear the CMOS.
There is no tangible system performance gain with DDR3 RAM by lowering the latency or bumping the frequency a few hundred MHz. so just run it at 1600 MHz. if it's stable and call it a day.
If your RAM isn't rated to run at 1866 MHz. it's no surprise your PC crashed and won't boot.