After New CPU, RAM Problem

Jul 2, 2018
2
0
10
Hi I have Hp Elite 7100 MT. I think my mobo 2a9ch unless aida64 or CPU-z saying that to me. My BIOS version 5.19 ı cant update lastes 6.18 version saying wrong BIOS. But first ı have 5.15 version then ı wanna upgrade updated 5.19 with no problem. Now my problem ı have i5 650 ı upgrade x3440. Now only work DIMM3 and DIMM4 slots. When ı plug old CPU all slot working perfect. I seen 12 GB RAM. When ı plug x3440 Aida64 and CPU-z seeing all RAM's but usable 8 GB or 6 GB only DIMM3 and DIMM4. How can ı fix this?