According to Norton Security System Support, I had neglected to upgrade my system from V5 to V6. Allegedly, V5 would no longer download all of the latest virus database info. This caused error 3047,53 that wiped out NSS V5, and several of my setting all of which had to be restored. I have now downloaded and installed NSS V6 and my computer is working okay except that it does not complete the boot process to the desktop - I get the Windows 7 logo and the Welcome screen with the stems and leaves, then it goes to a blank blue screen. I was able to launch the Task Manager that allowed me to enter explorer.exe to finish the boot to the Windows 7 musical chord and my desktop. The computer then works normally. This is bothersome to have to do at each boot and I am asking for advice on how to put explorer.exe in the correct location to cause a full boot to the desktop. Thank you in advance for your suggestions.