What To Do When I Cannot Uninstall AVG?

As my father is changing my antivirus program and firewall, he needs to uninstall AVG 8. When he goes through the dialogue boxes for uninstalling attempts to uninstall, he ends up with this error message:
Local machine: installation failed
Installation:
Error: Action failed for registry value HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows:AppInit_DLLs: creating registry value….
Error 0×80070005
Neither he nor I have any idea of this weird error message. I’ve tried contacting AVG support with no success. To be more specific, the AVG 8 is an AVG Anti-Virus free edition 8.0. But when there was a pop-up says WARNING there is an attack on his computer, it apparently leds my father to a screen with no way to exit out.
He has tried to uninstall it by going to the add/remove programs but it’s not even there. Next, I try installing a new one and then uninstalling it, however, that only uninstalled the new one. Here is how I finally get rid of this pesky thing.
Uninstall AVG thru Windows Add/ Remove Programs

1. Exit the program by opening Task Manager with Ctrl+Alt+Delete to end its process, AVGtray.exe.
2. Click Start menu and then Control Panel
3. Double click Add/ Remove Porgrams and navigate AVG
4. Click “Remove” to uninstall it.

This normally removes major part of AVG if not affected by other programs running on your computer. If you can find AVG folder at C:\Program Files or where it’s installed, it indicates that AVG is still in your computer and the associated files are still left in system registry. Therefore, need a more effective way to uninstall AVG and fully remove its associated files out of your computer,
Forcibly Uninstall AVG
The last option when you can not completely uninstall AVG is to force uninstall corrupted or left over programs files and registry information of it. Rather than taking the risk of manual removal, a Perfect Uninstaller has been is available and sophisticated in forcibly removing any corrupted, half-installed, half-uninstalled and hidden programs that Control Panel can’t detect or get around. Aside from that, it is designed to automatically scan the registry keys regarding of the removed program such as Norton Antivirus and users can decide if any them should be removed. It is recommended to always back up the registry before the force uninstall.