Greg, just a suggestion.
When you’ve finished the HijackThis cleaning of your system, deïnstall Norton.
When I bought my first pc, Norton came standard installed with it and caused very strange problems. This is due to the fact that Norton interferes with a lot of things in windows it shouldn’t do as an AV-program.
Once you’ve cleaned your system and properly deïnstalled Norton, search on your pc for everything that is called Norton and everything that is called Symantec and delete it.
Then, do a cleaning of your registry with a program like regcleaner (can be found here : http://www.worldstart.com/weekly-download/archives/reg-cleaner4.3.htm

After this please download Avast! and enjoy it.

Bye, Fast.