method 0: run chkdsk on the drive using another computer
mount the drive in another machine possibly with a USB hard drive interface and doing a
chkdsk e: /f on the drive (or whatever drive letter it happens to be).
your drive is probably due for a chkdsk /f about now.
method 1: using UNIX tools
if you are familiar with UNIX tools, you can boot system rescue cd (you will need to change the boot order) and mount the ntfs partition (once you have found the device path) and search your windows updates from the last to the first to see if there is a copy of this dll which has been updated. you only want to use the latest.
look for anything that ends with a number. it may be /dev/sda1, or if you have several partiions, it could be the middle partition (/dev/sda2).
mkdir /mnt/c /mnt/d /mnt/e
mount -t ntfs-3g /dev/sda1 /mnt/c
find . -name "NTDLL.DLL" -print
look through the list for the latest kb. then
cp /mnt/c/windows/system32/kb9.../NTDLL.DLL /mnt/c/windows/system32
umount /mnt/c OR
init 6 (shutdown)
method 2: mount the drive in another computer and copy the file
you can copy the files as you see in the steps above from one of the KB directories in \windows\system32 to windows\system32 or wherever the file actually belongs.
bring up a cmd shell.
cd \windows\system32 && dir /s/b ntdll.dll (or whatever file you have an error on)
copy that path to where it should go. make sure it is the latest version of the file. in the case of ntdll.dll, bit belongs in \windows\system32 and it may possibly have a copy found in \windows\system32\dllcache
or copy it from YOUR system restore/OS media if you are left with no files to copy from. you may need to use the microsoft EXPAND command to uncompress the file if the last character in the filename is an underscore(_).
expand d:ntdll.dl_ c:\windows\system32\ntdll.dll you don't want someone else's version of DLL's or it will cause breakage!
method 3: do a repair/rebuild
use your system restore partition or media (buy some if you don't have any, $20-50) to repair/rebuild/refresh your OS. you may lose your programs and registry entries, and programs that once worked may become broken, so you may have to reinstall (I had to). go through like you are going a typical install, up to the point where you choose to do the partition format, and it will give you the choice to format or Rebuild. choose R for rebuild. for HP media, choose rebuild/refresh or whatever sounds like it, it shouldn't reformat, but in case it does, have a backup of your data, hp is not predictable - old xp media only did format.