additional RAM

[andre3]

My desktop has an Asus P7H55-M/USB3 motherboard (intel i5, win 10) and actually just  6GB DDR3 RAM (1x 2GB, 1x4GB, Samsung).  If I try to expand that with additional 2x4 GB DDR3 RAM, the system won't start up.  Even if I remove the old DDR RAM and only use the new 2x4 GB DDR3 RAM (different brand). How come?

[Jiaszzz_ASUS]

Hello @andre3 

Thank you for reaching out to us.
ASUS has verified the motherboard for the best stability and compatibility when installed with the devices in CPU/Memory QVL list.
In addition to verifying if your newly installed memory is listed on the P7H55-M/USB3’s QVL, we recommend avoiding the use of different memory kits, as this can lead to potential compatibility and stability issues.
For further information, please refer to the "purchasing and installation guide" on the MEMORY/DEVICE SUPPORT page for the P7H55-M/USB3":

Ensure that all memory modules are from the same validated memory kit. Do not mix DIMMs from different memory kits—even if they are the same brand and model (e.g., two DIMMs each from two different memory kits). Mixing and matching DIMMs can result in a failure to boot and compatibility issues. In particular, the stability of a system with mixed DIMMs cannot be guaranteed when XMP (Intel)/D.O.C.P (AMD)/EXPO (AMD)/AEMP/AEMPII is enabled. For example, enabling XMP (Intel)/D.O.C.P (AMD)/EXPO (AMD)/AEMP/AEMPII to speeds above DDR5 4800MHz or above DDR4 3200MHz could result in an unstable system.

Thank you.