After 3 years is my computer now useless?

With new and faster computers today being so inexpensive you will find it difficult to get more for it unless you tried to part exchange it for a new one yourself. People are wary of buying second user:ok you may think it is all right for a beginner but then there is the problem with software if it is licensed to you or is it genuine in the first place. No reflection on you but I see so often someone has bought second user from an individual not from a shop that deals with refurbishments and they often have problems with counterfeit software. And of course, are you prepared to give a three month warranty? I personally, every time I am about to buy a new computer and 'get rid' of the oldest one I don't even bother trying to sell - I just strip it completely, put back the operating system and give it to charity.