1. Turn off your computer.
2. Press the power button to turn your computer on.
3. Hit F11 a few times quickly, while the launch screen is still up. This will launch the Recovery Manager. (If you see the Windows 7 boot logo, you've missed your chance and need to restart your computer and try again from step 2.)
4. On the left side it will say "I need help immediately". Underneath that there will be an option that says "System Recovery". Click on that.
5. There will be an option to either back up your files before restoring, or to recover without backing up your files. In my case, I'm recovering without backing up my files.
6. It will tell you to make sure all devices are disconnected from your computer. Make sure they are, and then click "OK".
7. There will be a "Welcome to the Recovery Manager" screen. Click "Next".
8. It will begin to reformat your partition and to reinstall the Windows 7 setup files. Once it's done doing that, click "Next". You'll be brought to a page saying "Recovery is Complete". After that all you need to do is reboot, and it will bring you through the wizard to set up Windows 7, just like on a new computer!
(Sorry for the terrible quality pictures by the way; I took them with my camera.)