The AVG Rescue CD is a portable environment that comes with a range of tools to help you clean up a virus-infected PC, fix hard drive problems, and get an unbootable system working again.
The system includes a version of AVG antivirus, which can update itself over the internet to be sure it has the latest virus definitions. There's also a Registry editor, a tool to check for and fix hard drive errors, and a capable file manager.
This variant of the rescue CD is intended for installation on a USB flash drive. After downloading, you should extract the archive contents directly to the root folder of the USB drive you'd like to use. (If you don't have a tool that can read RAR files, then try 7-ZIP).
Once this is done, check the README file you've just extracted for more instructions. And be extremely careful. If you don't follow those instructions precisely, then executing the archive's "makeboot.bat" file could corrupt your hard drive and prevent Windows from loading.
Keep in mind also that not every PC can boot from a USB flash drive, so this tool won't work in all situations. If you can't use it to start your PC then we'd recommend you try the ISO version of the rescue CD, which should boot any PC with an optical drive.