If you like, you could do a factory recovery to restore Windows 7 back to factory conditions. The link below from HP can help show you how to. Be sure to backup anything that you do not want to lose first though since it will format all of it.
HP Omni 220-1100 Desktop PC series*-* HP PCs - Performing an HP System Recovery (Windows 7) - c01867418 - HP Business Support Center
Hope this helps,