Hi Dan, Seems that the Avg files are damaged or corrupt if you cant remove or reinstall them.
Go to Start, Search, Files and folders. Do a search for AVG. Remove all files with the name (AVGGrisoft next to them). any files with AVGMicrosoft ie documents and settings LEAVE. as they could be shared. Then i would go to Iolo.com site (Google search) and download the version of System mechanic 7 as a free trial. Run this and it will remove all the system clutter and put your registry files in order.
Hope this helps