RAM slot questions

Does the first slot (A1) have to be populated for the computer to boot? Because when I tried this when I replace my CPU cooler and had to move my modules down to the second channel, the computer would turn on with a black screen and then the BIOS speaker would beep out some code or whatever then shutdown. So I bought a stick that could fit under the cooler and then it booted fine. Just recently the computer would start hanging up and freezing at random points from the post to windows log on or just hang up for a really long time (just turned it off at that point), so I reset the CMOS memory and that worked once, so I figured it was the first stick of RAM (which was really really crappy) so I checked it in my friend's computer, it worked fine, then we turned on mine to check a bare LED (not the most common use of the power supply, lol) and then it turned on and loaded windows fine. So we tried again and it did it 4 times now. So basically should I spend the money for new DIMMs or just leave it as is and hope it continues to boot and work?