Computers do not live forever
But my computer is only 5 years old. Yes! it seems like only yesterday you purchased it.
But like everything these days computers get old. Moving parts wear out and newer faster computer chips are developed. Those updates you must run to keep you safe etc. need more and more power and your old computer is now having a hard time keeping up.
So to keep up with the latest security requirements and run the applications you need you will have to accept the fact that 3 years is the designed lifespan of any computer desktop or laptop.