Some programs run, some do not

[dayo30]

Using Python 2.73, PyQt4 0n windows 7. PATH F:\Python27.

The sample graphs, downloaded from http://pyqwt.sourceforge.net/gui-examples.html,
work every time, from any directory.

The examples installed with the PyQt4 package also work every time.

My problem is that any other program which uses Qwt5; some from a Python book,
and some from internet sites, do not work at all.
The Windows command screen opens, and immediately closes.
No error messages.

I have tried everything I can think of, and getting nowhere.
It does not seem logical.

Any ideas?
TIA
Don Oliver