text: With adequate cooling and a reliable power source, your PC can be left on indefinitely. Obviously, PC components DO experience wear and tear, but a lot of wear and tear is actually induced by powering up and down the components. \n\nThe only danger in my opinion is leaving a PC on that is connected to an unprotected modem or telephone line. Lighting activity can damage your PC or modem. During thunderstorms, it is reccomended that you disconnect your PC and modem. \n\nOtherwise, go right ahead and leave it running. Server systems in major corporations run continuously and they experience only minor wear and tear. When inactive, your PC will hiberate or shutdown unused components, putting them into a sleep state anyway. \n\nBe aware that your PC is quite a large electricity hog, and will be drawing a considerable amount of power during its operational time, so if your electricity bill is your worry, then consider not doing it. :)