Sounds like youve got something nasty on your PC thats disabled norton and then locked you out.
Ewido found here click here can be run along side other av apps when you install it just untick the real time protection option, its a full 15 day trial and then reverts to a free scanner.
AS far as norton goes id probably uninstall and then if you want to put it back on do so. You need to download the removal tool from there website by the looks of it. click here for that try windows add/remove first thou.