motherboards Error 43.

[BullOwner1992]

Hello everyone I'm new here and I have a serious issue with my Acer M5100 desktop PC's motherboard. 

It gives me an Error 43 message on device manager when I use more than 3072mb of RAM this is very annoying because I cannot run high end games on that machine when only 3GB out of my 6GB is usable.
when I do assign the full 6144mb it comes up with Error 43 Windows has stopped the device because it reported problems. not only the GPU stops working but so does the audio and LAN. 

Here are the Specs on my desktop:

CPU: AMD Athlon X2 6000+ @3000mhz

RAM: 6GB DDR2 667mhz PC5300

GPU: NVidia GT440 1024MB GDDR5

HDD: 2X 7200RPM Conventional HDD's one 2,5'' and one 3,5''

PSU: 400watt