Can see 8gb in BIOS, but only 4 useable

Hi Nolube and welcome to Seven forums. From what I can see from the screen shots of your bios you have 8 GB ram installed. The system is disabling 4g of it as the first screen shot states 4096 Mb as the total ram. 2 of your slots are not enabled. Try removing and reseating the ram (with the power off). Check in the BIOS if there is a setting to enable or disable the second ram channel.

After following Indiantone's instructions, you might try resetting BIOS

F6: Fail-safe defaults
or
F7: optimized defaults

In the Start Search type msconfig to open the System Configuration window, if UAC asks, allow it to run. Select the Boot tab and click the Advanced button. The BOOT Advanced Options window will open.
Uncheck the box for Maximum Memory if it is checked. Click OK, Apply and reboot for the change to take affect.


Also run the WEI, Windows Experience Index.

You may find the setting under MIT, Advanced Memory Settings.
You may have a bad board too, run this exactly as told, i.e., RMA in different slots.

RAM (memory) test:

This will require memtest on a bootable CD or USB stick.
RAM - Test with Memtest86+

nolube said:

.....
Have tried updating the BIOS but the update files appear to be for 32-bit from here .. GIGABYTE - Motherboard - Socket 1156 - GA-P55A-UD3 (rev. 2.0)

Haven't tried resetting the BIOS though
.....

BIOS is not bit wise

Before updating BIOS try resetting to defaults. You have two slots that are not enabled. I don't see why that would be the default.

Did you complete Gary's post #4?

Let it run for the full 8 passes, unless you get any error, red lines at the bottom. If errors then go the single stick in each slot.

It shouldn't make a different, but Slot 1 RAM has a different part number unless it's a glitch in memtest.