I have a gigabyte H55M-USB3 w/ 2- 2gb 2000Mhz ddr3 Tried to replaced it w/ two 4 Gb 2000mhz ddr3 window 7 operating system won't continue to boot up. Replaced these 2000 MHz with 2- 4gb 1600 MHz but still same problem. Screen monitor stuck on 'starting window operating system'. Please help.