I can't understand why you are having so many problems with updating the BIOS and it must be really frustrating for you.
You can safely flash the same BIOS version and, for future reference you can also flash back to an earlier version if you wish to do so.
@BIOS should work in XP 64 bit have you downloaded and installed the latest version which is: B12.0723.1 and was released on 25/1012?
When you tried using QFlash:
Did you formatt your USB pendrive did through a Microsoft OS?
If yes and it was formatted as FAT32 did you plug your pendrive into a USB2.0 port on the PC? If it is recognised it will show up as a USB-HDD which can sometimes be confusing.
Is the pendrive 4Gb or less?
Have you tried a different make/brand of USB pendrive?
I have a Sandisk Cruzer pendrive which works fine for QFlash but the Sandisk Edge Pendrive I also have doesn't work on my system (go figure).
Sorry to go over the same ground but sometimes it is easy to miss a simple thing and, as I say, flashing the BIOS should not be causing you so much trouble.
EDIT: Was just about to post the above when I saw your update.
OK, double check that your RAM modules really are 4Gb sticks and not 4 x 2GB sticks.
Don't laugh, I made this mistake myself and it can easily be done with the way that RAM is sometimes labelled.
If they are definitely 4Gb sticks, remove 2 sticks from the system and make sure that the remaining 2 are from the same kit and are plugged into the DIMM slots numbered DDR3_1 & DDR3_2. Do you now see 8Gb of RAM?
If you do great, but if you don't move the stick from DDR3_2 to DDR3_3. Do you now see 8Gb of RAM?