ASROCK K10N78M Pro - Help Needed

[DKingOfDDamn]

I hope you can help me with my problem right now. I've been longing for any solution possible regarding this matter. Anyways, my name is Jhon. I have an ASRock K10N78M Pro MoBo updated Bios 1.50. I am using 2x2gb geil pc6400 800mhz memory card. the problem is everytime i install the other 2gb memory card on the dimm1 slot, my OS hangs (using Windows 7 64 bit). i've tried changing the dram voltage, but it still doesn't work. i've set the bios to defaults. it works perfectly on 2gb only, and have tried testing with the 2 dimm slots and found no problem with it. Can you please help me with my problem please. Thanks

P.S. No problems with whatsoever on the HDD and DVD Rom since it is new and proven tested already.

Thanks