Seriously though, barring factory defects, i think environment(heat, power quality) can be a factor. Sad to admit our server room is less than ideal.
One thing I always did with my PCs is equip them with ample RAM so there's less grinding due to the page file/virtual memory. I also made sure the page file was permanent in Windows PCs. I did it especially during the period from Win 3.0 to Win XP.