Your computer will need to be replaced more frequently than any of the peripherals you attach to it. The parts inside your PC--the processor, the memory, the hard drives, and the graphics cards--become outdated as more powerful parts are released and more intensive software apps are created to take advantage of the new hardware.

PC
A typical PC should give you 3 to 5 years of good use before you need to look for a replacement or upgrades. By comparison, though a monitor loses its brightness over time, it certainly won't need to be replaced every 5 years.

Monitor
CRT monitors are rated for approximately 25,000 to 30,000 hours of use. So if your CRT monitor is on for an average of 8 hours a day, it should last roughly 10 years before you notice a drop in its brightness (you can double those figures for flat-panel LCDs).

Keyboard and mouse
As long as you avoid spilling coffee or soda on your keyboard or mouse, those parts should last at least as long as your longest-lived computer.