Major slowdowns since update (100% memory, etc)

Since the automatic update a few days ago, I am experiencing major slowdowns on my computer. Looking at the Norton Security History, the slowdowns correspond to activities of Severity "Medium", Activity "Unauthorized Access Blocked (Open File)", Status "Blocked."

In the details section, the Actors have included "C:\Windows\System32\SVChost.exe" or "...Perform.exe" or "Conhost.exe," etc.and the Targets have all be Norton such as C:ProgramData\Norton\{....}, or "C:\Program Files (x86)\Norton Internet Security\...\Qbackup.dll",  etc.

I tried to do a System Restore to a point last week, but it fails (Blue Screen...).

Thanks for any suggestions on what to do.

Windows 7 Home, Dell Studio XPS