Having built two computers for personal use you want to have a high speed Processor, a large hard drive and alot of Ram, these should be accompany by a very good cooling fan.  Even though you have installed excellent parts in your computer by leaving your computer on 24 hours a day it not only causes heat build-up it also uses more energy than most people realize.  The number one enemy of any computer is heat.  Store your computer in a well ventilated area (DO NOT STORE IS A CLOSED CONFINEMENT)while operating.  Also, keep the room as cool and well ventilated as possible.