thanks for the answer.
What do you mean by "reset the firmware"? it's the latest one... The MB can't accept above-4G memory by default?
By reset the firmware settings I mean "reset the BIOS" or "reset the CMOS", those are just unfortunately common misnomers so I avoid using them.
Some motherboards have a pushbutton on the board which will do this, others require that you move a jumper. Consult your motherboard manual to find out how.
Some motherboards have problems with going from <=4GiB to >4GiB. It's a compatibility issue with mapping various other real addresses into the virtual address space. Once the settings are reset it should remap everything properly.