If you followed Dell's instructions you should have created a Win 7 DVD from the Windows copy on the hard disk. You need to boot from the DVD and do a Windows repair. This should fix the corrupted Windows files. Follow the instruction on the Dell screen to boot from the DVD. It's either F8 or F11 right after you see the Dell logo.
If you didn't make the backup Windows disk you might still be able to do a repair using the Windows hidden partition. You might want to check the Dell web site for instructions.