I see the board is for business users..just had a qwik look at the asrock site.
The board looks capable enough and is dual channell ddr3 up to 2200 speed.
There isnt a lot of detail in your post ie exact memory type(model no). for timings or anything or even to see if its in the compapability list.What processor u have psu n all but..amyway.
It seems youare able to get into the bios(UEFI) but dont know what to adjust.
Obviously you have to do this with one stick of memory in only.
Im also assuming your uefi is pretty standard and not changed for "business users" or even locked as asrock supplies to oem.
1. after u enter the uefi setup utility using del key or wotever
Use the arrow keys to scroll to overclock tweaker section.
scroll down to where it says dram configuration
Hit enter on that "folder icon" and check that the board is entering the correct timings for your memory,
There will be a load of boxes saying auto but beside those will be figues showing what the board is entering as the timings for your memory.
Make sure these match the stickers on your memory.
Most likely it will be something like 9-9-9-24 ,hopefully the secondary ones match too bu tthey wont be on the sticker.
If they dont match.. enter them manually yourself in the boxes where it says auto.
Then hit esc or the exit arrow to go back to the main oc tweaker section.
scroll down to where it says voltages.
scroll down till dram voltage is selected.
it should have a box with auto in it and a value beside it, which may..or may not be 1.50v
Ill digress a minute:
My original gskill ram was autodetected at a voltage of 1.59v, even tho it is supposed to be 1.50v,same as yours.
When I was running it at its standard speeds I reduced the voltage to 1.54v..I didnt go any lower cos..the ram sticks didnt seem that versatile and the board had already applied 1.59v.
Back to yours.
With the ifo you have supplied we dont even know if your memory has an xmp or extended memory profile or not.,however.
If the voltage beside auto is showing as 1.50,you may as u have suggested want to up it a bit to 1.59/1.6v "to be sure" hit enter or clik on the auto box and a selection of voltages should appear .
Select one.Dont go over 1.65v.
You now have a couple of choices, depending on whether you had to change the timings or not.
The simplest thing would be to hit F10 to save and load the changes,then boot into windows(if its installed,if it isnt just repost ,make surethe changes you made are saved and exit n shutdown)) with your 1 stick of memory.When windows has finished loading fully,hit shutdown.
Turn off everything turn off psu and monitor,press the power on button for 1min to clear any v's from capacitors etc.open up the pc insert the second memory stick and .. best case scenario both sticks will be recognised and off you go.
Things like xmp profile or not.Memory testing in case you got a bad stick,your psu type,whether the ram was seated properly,whether its compatable,cmos clears and so on are different q's.