Question XMP keeps going to default speeds

[taruneha]

My rig is
GIGABYTE Z390 AORUS PRO
INTEL I7-8700K
CORSAIR VENGEANCE 3000MHZ 8GB (2)
GIGABYTE B700H PSU
RTX 2070 8GB
COOLER MASTER LIQUID PRO 240ML

I've turned on XMP and the speed is 3000Mhz and after sometime it automatically goes 2133Mhz even while the XMP is turned on in BIOS. This is happening very frequently. And sometimes POST red light near DRAM appears and it halts boot. Again I've to change slots and then it'll turn on. Please let me know the problem and solution,..

 

[Fix_that_Glitch]

I would start with a memory check to see if you have a faulty ram stick.

 

[taruneha]

I would start with a memory check to see if you have a faulty ram stick.

Please assist me on how to check memory??