How to fix a damaged security file

A PC running WinNT4 SP5 cannot get past the logon screen … no error message. After booting from A: and running Scandisk, it was discovered that the “size of C:\Winnt\System32\config\security file is being misreported…”. Scandisk proceeded to “fix” the file and initially I was able to logon but a subsequent logon resulted in the same error and the subsequent “fix” did not fix it. Any suggestions aside from re-installing WinNt? The system has 128MB ram, only 183MB avail on C:, tons of space on D: