In some occasions, be it because you have reasons to suspect that the virus you caught has permanently damaged your system, because your PC is getting way slower than it used to be, or even just as a scheduled maintenance practice, reformatting your computer can be an useful way of 'cleaning up the mess' and regain all the computational speed your PC used to have when you turned it on for the first time. This article provides you with an easy step-by-step guide to make sure a smooth reformatting process.
As the first step, make sure you have a copy of the operating system you want to install, and all the installation files of the programs you need most, or at least make sure you know where to get them. You'll need to backup all the important data in your hard disk(s). Save all important files (a 'safe' choice is to backup the entire C:\Documents and Settings\
When you're sure you're good to go on to the next step, insert the CD/DVD of the operating system of your choice and restart. If nothing happens (e.g., the computer restarts normally), that means there is one little more step to go: when you restart, check the initial messages and press the right button to enter the boot devices setup screen (the button is usually F7, but it depends on the underlying system) and select the CD-ROM drive as the first device from which to boot -- you might want to roll back this setting once you're done reformatting).
At this point, your system will boot up from the CD-ROM. Follow the instructions carefully, particularly when you're asked to format your hard drive and delete all files on it -- if you're sure all the data is safe and backed up, go on with the OS installation. This will typically take one to two hours and requires little amount of configuration by the user (including assigning keyboard layout, system language, time, user names and passwords...).
Once the system is installed, you can remove the installation CD-ROM. If you wish, you can restart to change a setting so that even if you forget a CD-ROM in the drive, your PC won't do fancy things -- to do that, see the simple instructions above. Now, all you have to do is simply to take your backup unit and copy all the data back into the new system. Install all the programs you need, either from installers of from the Internet, and finally restart one more time (most program installations require restarting). If you're running on Windows, it might be a good idea to install an anti virus as soon as possible.
If you followed these steps carefully, your new system should be up and running as good as new!