Winlogon.exe - Ordinal Not Found

[Paul]

I have a laptop running Win XP that will not boot up.
When it is turned on the following message appears:

Winlogon.exe - Ordinal Not Found
The ordinal 644 could not be located in the dynamic link
library SHELL32.dll.

Then I click on OK and this message appears:

User Interface Failure
The Logon User Interface DLL msgina.dll failed to load.
Contact your system administrator to replace the DLL, or
restore the original DLL.

Then the only option is to click on a Restart button which
then brings me back to the original message.

How do I fix this?

Thank You

Paul