Two nice features of avast! antivirus protection are that it can be installed in Safe Mode and it will do a boot-scan before Windows loads. This makes avast! perfect for a computer which is is so heavily infected that it won't boot to Normal Mode properly.

Here are step-by-step instructions:

1. Boot to Safe Mode by starting up the computer and repeatedly pressing the F8 key.
2. Select 'Safe Mode With Networking' from the menu. Wait patiently for it to load.
3. Open the web browser and navigate to http://www.avast.com/eng/download-avast-home.html
4. Click the 'Download Now' button.
5. Install avast! and get the latest updates for it. If you are unable to update it, go to http://www.avast.com/eng/updates.html to download and install the updates manually.
6. When it is finished installing, it will ask if it should do a boot scan. Make sure you select this.
7. Reboot and let it scan. If it finds an infection it is suggested to use the delete all option and then wait patiently for it do find and remove what it can.
8. After it completes there is a chance that Normal Mode will work again. avast! can now be un-installed. If it is preferable to leave it on the system then the original anti-virus program should be removed.
9. Use SpyBot Search & Destroy and MalwareBytes Anti-Malware to remove any other undetected infections.

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