I've searched for and found other instances of my problem on here, but the answers given weren't helpful to me, so here goes:

I have an install of Windows XP Pro that failed to boot, with an "Operating System Not Found" error, after a software install. I've slaved the HDD with another running XP to run a virus scan, defrag, and check for errors. Virus scan came back clean (AVG 7.5 Free Edition, fully updated), and the Windows disk check utility didn't report any errors (I don't remember if it automatically reports or not. I miss the old DOS scandisk!). Apparently, the disk check did do something, because it then booted to a screen saying that "<windows root>\system32\hal.dll" was missing or corrupted, and advising me to reload it. I did that by booting into the recovery console with the XP CD. Then got a message that "<windows root>\system32\ntoskrnl.exe" was missing or corrupted, so I reloaded it, too. After that, I got a message that "Windows could not start because of an error in the software. Please report this problem as: Load needed DLLs for kernel." What I need to know is, which DLLs is it referring to, so that I can load them?

At his point it sounds as though the entire XP Pro installation is totally shot. Can you boot to safe mode? Even though you were capable of restoring specific files from the recovery console you might want to list the contents of the system32 folder using the recovery console. This is where windows stores the majority of the OS. My system32 folder contains 2,413 files not to mention 262 sub folders that contain an additional 4,470 files. If the system32 folder is toast the best option you have available is to use another system to copy and save all of your user data and do a clean install of XP.

The other option available is to reinstall XP over the top of what you currently have using the repair http://www.michaelstevenstech.com/XPrepairinstall.htm option. The problem with this approach though is it does not clean up the registry and it overlays any maintenance you have installed on XP up to this point.