Pc only recognizes 8gb of 16 gb of ram

Must the second DIMM go into slot #2 ?
I had a PC where the second DIMM went into slot #3.
Don't ask me why.

Check what version of BIOS you have on the CPU-Z Mainboard tab.

Version 1.40 description shows a "Memory Patch":

1. Improve system compatibility.
2. Patch Crucial DDR3-4G-1600 and APACER DDR3-1G-1333 memory.
3. BIOS [Case open] option default set to disabled.
4. Improve Windows compatibility.

On this ASRock support page: ASRock > H81M-HDS

Layback Bear said:

bigboi972 let me see if I understand you correctly.

Both new ram modules work in one of the motherboard slots.
Neither new ram modules work in the other motherboard modules.
When installing both ram modules the system only shows one.

If this is true and the bios are set to default in my opinion your motherboard has a bad ram slot.

precisely you are absolutely correct

DavidW7ncus said:

Check what version of BIOS you have on the CPU-Z Mainboard tab.

Version 1.40 description shows a "Memory Patch":

1. Improve system compatibility.
2. Patch Crucial DDR3-4G-1600 and APACER DDR3-1G-1333 memory.
3. BIOS [Case open] option default set to disabled.
4. Improve Windows compatibility.

On this ASRock support page: ASRock > H81M-HDS

I will look into this asap

Mellon Head said:

Did the computer make any beeping noises when you did that?

I did not notice it I doubt it considering the bios does not come up on screen . I built this pc their was a little speaker i never connected it which is possibly why I never heard as beep i posted a picture of it.

bigboi972 said:

Mellon Head said:

Did the computer make any beeping noises when you did that?

I did not notice it I doubt it considering the bios does not come up on screen . I built this pc their was a little speaker i never connected it which is possibly why I never heard as beep i posted a picture of it.

Correct, you won't hear the beep codes unless you connect that little speaker.
Is it easy to get to now so you can install it?

DavidW7ncus said:

bigboi972 said:

Mellon Head said:

Did the computer make any beeping noises when you did that?

I did not notice it I doubt it considering the bios does not come up on screen . I built this pc their was a little speaker i never connected it which is possibly why I never heard as beep i posted a picture of it.

Correct, you won't hear the beep codes unless you connect that little speaker.
Is it easy to get to now so you can install it?

I am sure it is i will have to check my motherboard manual