Another thing, I think my 2nd slot is broken. After using this for 2-3 years, my computer wouldn't turn on and took me a while to figure out that if there is a memory stick in it, then 99% of the time you will not hear the boot up beep. I then took the 2nd slot memory stick to the 3rd one.
Go to http://www.memtest.org/ . Download the "Pre-Compiled Bootabel ISO". Burn it to a CD. Then restart the computer. Enter BIOS, and change the boot order to boot from the CD drive first. Then restart and let it work.