i had this problem with a gateway computer, i dont know why but i whent to the bios and disable everything, usb, sound, paralel port, network, and it worsk fine for me, dont disable the video... let me know if that fix the problem 
, if that doest work, open your computer and check if the pins of the memory doest have any scrach or something and clean the dust. let me know if this doest work. it can be a few thing but we can fix it :p
, if that doest work, open your computer and check if the pins of the memory doest have any scrach or something and clean the dust. let me know if this doest work. it can be a few thing but we can fix it :p