As CHill60 discusses read the documentation on the call. If you are going to play on the Win32 API at least bother to read the documentation on the calls
http://msdn.microsoft.com/en-us/library/windows/desktop/ms724942%28v=vs.85%29.aspx[
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Remarks
The calling process must have the SE_SYSTEMTIME_NAME privilege. This privilege is disabled by default. The SetSystemTime function enables the SE_SYSTEMTIME_NAME privilege before changing the system time and disables the privilege before returning. For more information, see Running with Special Privileges.
The function also has error return via GetLastError to confirm the problem.