int ret = DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_IB), hwndParent, InputBox_WndProc);
Why id doesn't show any Dialog?
Why should it show anything?
Does IDD_IB template exist?
What is hwndParent? Is it a valid handle?
What is InputBox_WndProc?
You have to debug your code to be sure all the parameters passed in the DialogBox(...) are valid!
And of course you have to use GetLastError (as S_M_A already mentioned) to obtain the extended error information if some error happened.