Second both suggestions above.
Heard very good reports concerning the more recent versions of Norton (since 2010).
Even if not activated, a "dormant" installed AV is still "active", and will cause interference with another installed one.
Best clean them both with the specific tools (I haven't heard of finaluninstaller; I would think the removal tools provided by the respective companies should be adequate) and give the machine a jolly good reboot, then install the AV of your choice.
If it were me, that would be (and is) Avast.
Other good free ones include MSE, and Avira.
Good pay ones...you already had one installed.