Did you delete the Recovery partition? Try running Recovery by using the key given on first bootup screen. If you are able to recover, use these steps: Dual Boot Installation with Windows 7 and XP
If you cannot run Recovery, you'll need to find a Windows 7 installer for your version to reinstall, or contact you manufacturer's tech support to get the Recovery Disks. You could have made these Recovery Disks from the Recovery partition before you disabled it, just as you could have made a Windows 7 backup image to reimage your HD in 15 minutes.