In order to investigate your problem further we need to rule out Norton.

Option 1: is to uninstall Norton (just to make sure it is not causing the problem) and install one of the programs suggested by Ztrucker.
If you install a standalone antivirus ensure you install a firewall as well.
Option 2: if you have paid for Norton then you need to contact their on-line support giving the
Symantec Shared Component , cltlmh.exe, error and see if the can offer any suggestions
as to the cause of this error.

Jim