A laptop does not need a dramatic blue screen or a completely dead battery to deserve retirement. Sometimes the warning signs look much less impressive: a browser that takes forever to cooperate, a fan that sounds like it has personal grievances, or a battery that seems to disappear before lunch.
That creates a tough buying decision. A new laptop can cost plenty, while an old one can still perform basic tasks. The question is not simply whether the machine still works. It is whether the machine still works well enough for the way it gets used now.