It depends. If you PC is faulty, it can be repaired, then you need to replace.When should you always upgrade to a new PC? I figure every 4-5 years would suffice. Do you agree? We can upgrade our computers to keep working for years to come, but new PCs come out, along with new parts, and the old ones tend to become obsolete. Anyway, how often would you say you upgrade or buy new computers?
It also depends on what you do with your PC too. For example if you want to go in to programming, and you don't have a good enough PC, then you should change.