Lot of opinions about browsers and AV software but very few people responding to the OP's question about the differences in the two PCs.
We are all waiting for your response to his question Dave........
With the small amount of info provided, it would be hard to provide a realistic diagnosis. But if the OP did get rid of Norton, install a good AV program and do a full sweep, it would probably cure his problems....
Guess you missed my request for their mail client info!
Spam is email you don't want. You usually handle that through your email provider, supplying enough information about what you want to see, and don't want to see, that spam goes off to another mailbox you can choose to look at, or not. Anti-virus programs do not usually filter your email for what you do or do not want to see, but some will check email content for what might be dangerous.
An advertisement showing up on a web page you are looking at is an advertisement. Ads what pays to keep a web site going. Anti-virus programs do not normally block web advertising, but there are ad-blockers that can prevent certain web advertising technologies from working.
Web advertising tends to be user targeted, based on your browsing history. If you see more ads on the same page from one computer than another, the web site furnishing the ads is working with different information from different histories. Or one computer could have an effective ad blocker running.
Norton used to be the industry standard for protection and file maintenance. USED TO BE.
Now its an evil piece of software used to slow computers down to the point that PC owners buy new computers when they didn't need it. Use any other virus protection to solve your problems.
I suspect that most negative Norton comments come from those that have not used the product in years and love to bash a product based on some experience years ago believing that a product never changes or improves. I work for a large defense contractor and we use Norton on all our networked PCs. We use Norton Internet Security on all our PCs/laptops at home. We buy the 3 license version at Sams for $50 rather than renewing at a much higher price. Our PCs use either Windows XP Pro or Windows 7 64 bit. In addition I checked PC Magazine and found it gave Norton good reviews.