The received wisdom, which you will see in many places on here, is to remove Norton (not easy, because it sprays its stuff all over your computer), and to use one of the FREE alternatives (I use AVG, which has been flawless for several years, but other folks speak highly of other packages).
The sequence is:
1. Find and print off the instructions for removing Norton (search in here will find 'em)
2. Download AVG (or whatever) installer.
3. Disconnect from the internet
4. Remove Norton
5. Install AVG
6. Reconnect to the Internet and tell AVG to update itself.
7. Continue your Internet life with a far faster PC.