How do I know what rev is it? I tried changing via AI tweaker only. and there is no DOCP option in mobo. Actually if I install 3 rams, it will read as 2666 mhz. But when I put the last ram, it will beep 3x and wonr boot. So I tried resetting the cmos, but didnt work. When I changed the ram to 2133 l, it worked. Now, I cant change anything. It will just revert whatever changes I do with the ram.
With the 4th DIMM it's trying to enable dual channel but dual channel is more demanding on memory controller with 4 DIMM's so it fails down to a default DDR4 clock speed. It's more difficult to get 4 DIMM's working at higher clocks and requires frequent CMOS resets, usually after any time it fails to train and restarts. When you reset CMOS always do it with both pulling the battery and shorting the reset pins.
One thing to do is try manually setting a DRAM voltage, I'd try 1.4V to start. You can try reducing it if that proves successful but DDR4 memory is safe up to 1.5V, although not over 1.4V in 24/7 use unless you have certain ram chips and you know it.
If you don't know your BIOS version you've probably never updated so it's a good idea to since updates quite specifically brought improved memory compatibility and stability. It should tell you BIOS version in the Advanced Mode/Favorites screen.
In the end, you may never achieve rated DIMM clock speed with 4 DIMM's unless you wade into the dark world of tweaking with memory timings. That's why most people just stay with a 2 DIMM arrangement in their systems.