If you have the install DVDs, you should reinstall the ntdll.dll from them.
Therefore you'll have to rename the corrupted ntdll.dll to "ntdll.dll.old" then restart your computer with the DVDs and run a repair install
Try also a System Recovery Options
or System Repair Disc
(if you don't own the DVDs)
It looks quit tough to manage but if you follow instructions, you should be fine.
If your using Firefox, some says to enable cookies in the Tool =>Options=> Privacy tab.
Could be Software CD/DVD Burners (Daemon Tools) or Graphics drivers
to reinstall/update. Also Winamp and Winrar. The list is quit long...!