If you are running Windows XP and the shutdown button is missing from the login screen, the first thing to check is whether or not the local security policy has it disabled. If you are working in a company environment, this might be a policy that is pushed down from the system administrators through a Group Policy and you might not have access to change the local setting.
If you are receiving an error that the "polstore.dll" file is missing or corrupt, go to the Error Fix section first and follow the steps to attempt fixing it.
If you receive the error: Failed to open the IPsec policy storage. The following
error occurred: The system cannot find file specified. (80070002) when trying to open the Local Security Policy from the Administration Tools, try doing the following to correct the issue, then attempt to follow the steps above for changing the security policy setting.