The only computer I've ever worn out was my first "real" box, a Mac Plus that I acquired in 1993. After a few years of faithful service, a design flaw reared its head (no fan => hot computer) and killed the power supply. Fortunately, replacement power supplies were easy to come by back then, so a quick swap made everything good as new. That computer continues to function even today, albeit more as a curiosity than a workhorse.