windows wont start because of missing or corrupt files what do i do

What is the exact error message?

If it looks like this:

Windows XP could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SYSTEM
Windows XP could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SOFTWARE


Then try this:

http://support.microsoft.com/kb/307545