This tutorial is for Windows 7. I may modify it to include Windows XP instructions in the near future.
You can only use this method when your computer starts up normally so restart your PC if it's in safe mode. You're then going to open the start menu and Right-Click on "Computer", then click on "Properties" at the bottom of the menu.
After the next screen comes up, click on "System Protection" on the right side of the window. It's highlighted in blue and underlined below:
Next when the window below comes up, click on "Configure" which is highlighted in blue below:
Ok, you're near completion. The next thing you need to do is click on "Delete" which is highlighted in blue below:
You're pretty much done. The last step now is to click "Continue" when this window comes up and you're done:
Now that wasn't too hard was it?