One of the first things that I was taught by an Olde computer tech, was to NOT unplug the power cord. Make sure that power is off, but leave the power cord plugged in the outlet. This would assure that the system stays properly grounded. HOWEVER, I never felt comfortable with this, having gone through some electronics labs prior to that, so I also would echo unplugging the system. My hint is: after sticking the RAM in its slot, gently grab each corner of the installed memory and pull up, this makes sure that the little clips are completely seated (which means that the RAM is fully seated, as well.) If it comes back out with a gentle pull, then try again. Yeah, easy, 2 minutes, tops, even if you're ham-handed like me.