Ropes should be replaced at least every 5 years;carabiners and other metal equipment should be replaced if it has been dropped, as a fall can create microscopic fractures that will weaken it. Check over your harness and look for wear on the nylon straps.

If your carabiners and the like have not been dropped but just left in storage, they are probably still good. If your harness does not have any wear points, it is probably still good. Use your own judgement; aside from ropes, rock climbing equipment won't go bad from being in storage. But if you are unsure about the history of the equipment, I would replace it.