[1] ...My free trial period had not expired when I uninstalled Norton. After uninstalling I then ran the Norton Removal Tool from the net, however I had installed AVG by that time. Would that have made such a difference?
[2] Perhaps I need to do a clean install of Windows, but worried i could make it worse...
A1. Yes, indeed! Norton (and McAfee) applications are notorious for not uninstalling cleanly. If you didn't run the removal tool before you installed AVG, chances are AVG didn't install properly and therefore hasn't been working properly either, hence
your "can't install updates" problem.
A2. Yes, I'd say a clean install is an excellent idea at this point. See...
Cleaning a Compromised System
http://technet.microsoft.com/en-us/library/cc700813.aspx
Back-up any personal data (none of which should be considered 100% trustworthy at this point) then format the HDD & do a clean install of Windows. Please note that a Repair Install (AKA in-place upgrade) will NOT fix this!
• How to back up or transfer your data on a Windows-based computer
http://support.microsoft.com/kb/971759
HOW TO do a clean install of Win7: See the "Using the Custom installation option and formatting the hard disk" (or the "Reinstalling Windows 7") section of http://windows.microsoft.com/en-us/windows7/Installing-and-reinstalling-Windows-7
NOTE: If your computer didn't come with a set of disks, there will be a hidden Recovery partition (not to be confused with System Restore) you would use to do the clean install (AKA a "destructive recovery").
After the clean install, you will have the equivalent of a "new computer" so take care of EVERYTHING on the following page BEFORE otherwise connecting the machine to the internet or a local network (i.e., other computers) AND BEFORE connecting a flash drive, SDCard, or any other external drive to the computer:
4 steps to help protect your new computer before you go online
http://www.microsoft.com/security/pypc.aspx
VERY IMPORTANT!! => The Norton free-trial will be reinstalled (but invalid) when Windows is reinstalled. You MUST uninstall the free-trial AND download/run the**Norton Removal Tool** (again) BEFORE installing any updates AND BEFORE installing your new anti-virus application (e.g., Microsoft
Security Essentials - free).
Also see:
Risks & Benefits of P2P file sharing
• http://www.microsoft.com/protect/data/downloadfileshare/filesharing.aspx
• http://blogs.technet.com/mmpc/archive/2008/10/06/the-cost-of-free-software.aspx
• http://www.us-cert.gov/cas/tips/ST05-007.html
Steps To Help Prevent Spyware
http://www.microsoft.com/security/spyware/prevent.aspx
Steps to Help Prevent Computer Worms
http://www.microsoft.com/security/worms/prevent.aspx
Avoid Rogue Security Software!
http://www.microsoft.com/security/antivirus/rogue.aspx
If you need additional assistance with the clean install, please begin a new thread in this forum: http://social.answers.microsoft.com/Forums/en-US/w7repair/threads
If these procedures look too complex - and there is no shame in admitting this isn't your cup of tea - take the machine to a local, reputable and independent (i.e., not BigBoxStoreUSA or Geek Squad) computer repair shop.
Wish I'd had better news for you. Good luck!