CentOS only detecting 50% of ram on IBM Server

When did this server show 16GB of RAM and when did it show 8GB of RAM?

I'm assuming this is not a new installation because you're using a kernel that's over 1 year old. Can you run updates? My general recommendation would be to update your system's kernel (and OS), since that's just the right thing to do, and you're on the base kernel of CentOS 6.4...

Edit:

A closer inspection of your kernel boot command shows that you've reserved almost 8 Gigabytes of RAM for your crashkernel.

kernel /vmlinuz-2.6.32-358.el6.x86_64 ro root=/dev/mapper/vg_livecd-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=vg_livecd/lv_swap rd_NO_MD rd_LVM_LV=vg_livecd/lv_root SYSFONT=latarcyrheb-sun16 crashkernel=8128M KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet

The recommended value for a system of your specifications is much lower.

The amount of reserved memory is either determined by the user, or when the crashkernel=auto option is used, it defaults to 128 MB plus 64 MB for each TB of physical memory (that is, a total of 192 MB for a system with 1 TB of physical memory).

Remove the "crashkernel=8128M" or set the crashkernel value to "auto" and try again.

How did this value even get set in the first place?