Sky
If you use Norton Internet Security, do a search on your PC for "Norton Internet Security.txt". If it exists, that file will have your serial.
Also, once again, do not believe the instructions that Norton say for removing their stuff. The Norton Removal Tool does NOT remove Norton fully, there are bits of it left all over the place which you have to remove manualy, especially in the registry. Do not believe the so-called instructions on the link provided by Dazdaz