I have a slow-running Dell that's about five years old. It has been protected by Norton Symantec throughout its life and, after a recent full system scan, Norton declares it to be in good health with all threats under control. On the other hand, I am told that slow running is what happens when a PC is full of viruses, and I should consider reinstalling Windows. Which of these is right? And if my PC is clogged up, what is the point of Norton Symantec? It would be nice to be able to make an accurate diagnosis……..