I had my computer built in January 2008. In early 2009, I had to have a new power supply which I had installed at a different place from who built the system. My computer is in the shop again having another power supply put in. I am not sure what quality psu was in it, but I have asked to have a better quality one installed this time. My question is, how long should they last? I always thought about 4 or 5 years.