Can't boot your computer, and think the problem is malware? Boot a live CD made specifically for scanning your computer without starting Windows. A live CD is a tool that boots completely from a CD or a flash drive, meaning you can use these tools whether Windows is working or not. A variety of live CDs exist that make it possible to scan your computer for viruses.

Recently I wrote the manual 50 Cool Uses For Live CDs. In this manual I pointed out a variety of different disks made specifically for scanning for viruses. Five such tools are highlighted in the manual; find out about three of them below. Be sure to download the manual to read about the rest!

BitDefender

Perhaps the best-known live virus scanner, the BitDefender live CD removes viruses when all else fails. This tool, which uses the same definitions that power BitDefender's desktop scanner, runs on a version of Xubuntu.

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Start the CD, update your virus definitions, run a scan. It's simple to use, so get started.

There are a number of other applications included on this disk, so it's worth exploring a little bit. The disk also has access to Ubuntu's repositories, so you can also install any of the thousands of programs if necessary. Read more about BitDefender's Live CD.

Kaspersky

Known for it's excellent scanning on the desktop, Kaspersky also comes in live CD form. In some ways this tool is less straightforward than BitDefender; you'll need to remember to update yourself instead of being prompted, for example. Still, this is a well done tool that can catch a lot of malware and clean it up.

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There's not a lot on this disk besides the virus scanner, but what else do you need? Read more about the Kaspersky Rescue CD.

AVG

Like AVG, and trust its protection? You should check out the AVG live CD. Unlike the above tools, AVG's live environment does not include a GUI. Instead, you'll find a text-based interface:

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Don't be frightened, it's easy to use. Just use the arrow keys to make your selection. Run a scan, then clean up any malware you find. You'll want to run an update first, of course. It's also worth checking out the "Utilities" section of this disk, as it contains a bunch of useful tools including a file browser ("Midnight Commander") and a program for recovering deleted data.

You can read more about this CD, and find a download on AVG's official Rescue CD page.

Conclusion

There you have it, three free online antivirus scanners you can run when Windows won't boot. You can find more such tools, and a lot of information about live CDs, in our live CD guide, so be sure to check it out. Avira and Panda's live environments are both linked too.

Oh, and a tip - you can combine all of these tools, and many more, onto a single flash drive using YUMI, a tool for booting multiple live CDs from one USB disk.

Do you have any other suggestions?  If so, please leave them in the comments below. I love discovering new tools.