Dell has a boot Save config Sector on your Dell Hard drive - That's why you don't have the orginial Copy of Windows (unless) you called during the time of warrenty and they would have sent them to you (U HAD TO ASK FOR IT) - When going back to the boot config on your dell it will revert to the day it was created - Losing everything except the operating system and soft ware you ordered at the time.
To boot it Restart the PC When you see the dell logo Press F10 and it should give you a warning about turning back the software clock. and losing your data files (not the win7) - The F key may be different SO I suggest if F10 doesn't do it - Start with F1 and go one at a time.
If you take the drive out and put it in a usb Dock and connect it to another PC you will see how it is sectored off - That's why dell after 2010 stopped sending oem disks out (cost cutting Shipping) and they can get you back to square one if a problem comes up. Forgot to add you can also go here
http://en.community.dell.com/?~ck=mn
And Get user help on your Dell product model and finding the correct F key to get you OPS back
Hope these helps you