DDR4 RAM Problems need help

[Koce662]

Hello everyone i have a problem with my PC here it go, i build this PC 3 days ago i didn't have any problem i run AIDA64 for 12 hours played Witcher 3 for couple of hours and everything was fine overclocked at 4.2GHz RAM 3200GHz at XMP but yesterday while playng it started crashing i thought its because of the GPU so i put it in stock setting and it was still crashing then i run AIDA64 and it Failed the Stress Test when i run it only on Stress CPU everything is fine but on Stress cache and Stress system memory it fails, i did some research i sow that my i7-6800k supports only 2400GHz DDR4 so i turn off XMP and set the RAM at 2400GHz at 1.24v and everything was running perfectly

 

Except now it doesn't detect all 4 Dim slots it shows only 3 but still 16GB i don't know why.

 

I try to set it on Auto but it crashes before even loads the BIOS so now i don't know what to do how to set it up so it shows all 4 Chanel's i could't find any answer online so if someone can help me ill be grateful

 

Here some more Screenshots