Stick the XP CD in the drive, reboot, and follow instructions is the easiest way. Just be sure to format when given the option, or you're going to have two listings for XP when you boot.
But before you do, either download a copy of SP2 (the full thing, not the downloader) or order the SP2 CD and be sure that is installed BEFORE you connect to the Internet. If you can, make a slipstreamed install CD (instructions can be found on numerous sites around the Internet)
Then hit Windows Update and install all crittical updates, reboot and head back to Windows Update to make sure there aren't any more crittical updates. Reboot and repeat until you no longer have any crittical updates to install.
The next step is to download a browser besides IE. I personally like Mozilla Firefox, but there's also Mozilla proper, and Opera. Download one, two, or all three, and then bar use of IE for anything but Windows Update. You should also use this opportunity to find an email client besides Outlook Express if necessary. This will go a long ways to prevent the problems from happening again.
You also want to make sure there's an up to date virus scanner installed. If you need a free one, you've got AVG Free, and Avast for choices.
At this point, you should also make seperate accounts for the kids and your friend. Make sure the kid's accounts are limited user accounts so they can't install something that will ravage the entire system. You can set up games and other programs from an admin account.
These simple steps will go a very long ways towards preventing another such occurance.
A friend asked me to re-format his hard drive, so he could get rid of a million problems caused by things his kids installed on his PC. He's running XP Home and his computer is running very slowly and he gets pop ups continuously. I've tried turning things off and running a pop up blocker along with running a spyware program and cleaning out the spyware with no success in fixing the problem. Can anyone give me clear instructions on how to re-format the hard drive? I've tried to accomplish this but XP won't allow it. I keep getting a message that some programs are running and I can't turn them off.

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