Reset the CMOS memory the right way as is described in the motherboard manual using the clear CMOS link with the power cord unplugged.
And when the battery is out, press the power button to discharge all the electricity from the system. How To Clear CMOS @ http://pcsupport.about.com/od/fixtheproblem/tp/clearcmo...
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.