There's a couple of things you can try.
Boot up into the Advanced Boot options - select Repair your Computer and navigate to the Recovery Environment.
Select Command Prompt and enter
bcdedit |find "osdevice"That is a Pipe symbol before find.
Using whichever partition letter it gives - enter
chkdsk x: /f where x is the partition letter.
If that doesn't resolve and your install disk includes SP1 then boot up with that, press enter with Windows Set up (EMS Enabled) highlighted and again navigate to the Recovery Environment to select Command Prompt.
You already know the partition letter, so enter using that partition letter (assuming C) -
sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows and see what that reports.
That should replace the missing .dll but this article will show you how to extract the .dll from your install disk.
http://www.sevenforums.com/tutorials/42776-extract-files-windows-7-installation-dvd.html