New Memory Computer won't boot windows

Question

I am running a MSI A58M-E33 running Windows XP
AMD A Series A4-6300 - 3.7 GHz - 2 Cores - 1 MB Cache - Socket FM2 - Box - AD6300OKHLBOX
It came with Memory of
ADATA XPG V1 4GB Desktop Memory Module - DDR3 1600, PC3-12800, Blue - AX3U1600C4G11-SD
It's been running fine since December. I decided to add another memory component. So I bought a duplicate ADATA memory stick
Now my computer is saying
CPU or Memory Changed !!!! Please enter setup to configure your system.
Press F1 to run setup.
Press F2 to load default values and continue.
I tried F2 and it goes to load XP and then ask to run in safe mode or normal. I don't see what options to select in the bios for memory. Is there an option to choose what it loads?
I tried taking out the new memory and just using the old memory and it still has the same problem. Same problem with just the new memory or just the old or both together it fails to load. I can access the bios but am unable to load the preinstalled windows os.
Do I have to reinstall windows when installing new memory? I could have sworn the last time I did this on another computer it started no problem.
The only strange thing is though the memory looks the same on the outside. Same stickers same pictures same colors. When I explore my board the old memory is labeled.
DDR3 memory slot 1: DDR3 SDRAM - Kingmax                                          EWB4GB681CA3-16IC
And the new memory is labeled
DDR3 memory slot 2: DDR3 SDRAM - A-DATA                                            DDR3 1600
Both say A-Data on the physical memory so I wonder if I was swindled on the original and it really isn't A-Data. 
So what should I do?

Answer 1

Windows XP (non-64 bit) can only detect up to 4 GB of memory.
HOWEVER....a 32-bit system will shadow various memory from the end of memory back towards the beginning. Things such as your video card memory and other various memory components will be shadowed.
On top of that, if you are using the on-board video, the memory allocated to it will start at the 4GB point and work towards the beginning. So if you set it to use 1GB of memory, it will reserve 1 GB of system memory for use with the video card. In that case, you would only have 3GB available. Add in other shadowed components, and you might be at 2.96 available.
All in all, for a 32-bit system, this isn't surprising. Many people don't remember those days, but us old people do.
I would consider upgrading to a 64 bit based OS before going further.