You might experience problems when mixing and matching RAM kits, as you are. This is why RAM comes in packets, so that
the manufacturer can make sure they work together. In addition, VRAM is RAM for GPUs, it's not system RAM. You'd be better
off buying an actual GPU, if this is a desktop system. Otherwise yes, check around in the BIOS for display memory. You can
do a dxdiag afterwards to see if it works.