If you wipe the HD you'll not be able to run factory Recovery, which is on a partition unless it has been deleted or damaged. I would try to make the Recovery Disks first so you have a backup method.
If this fails, you'll need to call eMachine Tech support to order recovery disks, or find a Windows 7 installer for your version to clean reinstall with the Product Key on COA sticker.
Or you can go through the active User folders, Select All and delete all the files, then Uninstall programs as desired in Control Panel>Programs and Features. When it's done clean it up with CCleaner followed by Windows 7 defragger.