Reboot in NT

Try to read on in the docs. You need to enable some privileges in your access token. See :
GetTokenInformation(), TOKEN_PRIVILEGES, SetTokenInformation() and so on.
When you have enabled that SE_SHUTDOWN than you should be able to reboot.

I have tried this and did not work, any idea ?

// Get a token for this process.
 
if (!OpenProcessToken(GetCurrentProcess(),
        TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken)) {
                 wsprintf(szBuf, "OpenProcessToken Error #%d", GetLastError ());
        MessageBox(NULL, szBuf, NULL, MB_OK);
    }
   // error("OpenProcessToken");
 
// Get the LUID for the shutdown privilege.
 
LookupPrivilegeValue(NULL, SE_SHUTDOWN_NAME,
        &tkp.Privileges[0].Luid);
 
tkp.PrivilegeCount = 1;  // one privilege to set    
tkp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
 
// Get the shutdown privilege for this process.
 
AdjustTokenPrivileges(hToken, FALSE, &tkp, 0,
        (PTOKEN_PRIVILEGES)NULL, 0);
 
// Cannot test the return value of AdjustTokenPrivileges.
 
if (GetLastError() != ERROR_SUCCESS){
                 wsprintf(szBuf, "Erro AdjustTokenPrivileges #%d", GetLastError ());
        MessageBox(NULL, szBuf, NULL, MB_OK);
    }
 //   error("AdjustTokenPrivileges");
 
// Shut down the system and force all applications to close.
 
if (!ExitWindowsEx(EWX_SHUTDOWN | EWX_FORCE, 0))
    error("ExitWindowsEx");

Adjusted points to 100

The code seems ok to me (but I havn't done this before). Have you tried to use GetTokenInformation() to look at your privileges? What happens if you are stepping through the code in the debugger?