Dialog not processing messages

I have a dialog based machine control application that runs in a do-while loop until the operator pushes a hardware stop switch. The program uses PCI boards and their associated DLLs.

I need to provide a software pause button (dialog control) but the app will not process the button method when the control is clicked. All I get is an hourglass and "Program Not Responding" in the title bar. The same thing happens if I try to activate a radio button on the form.

Is there an API function that I can call at different places in my code to force Windows to momentarilly suspend my code and go do its normal messaging stuff?

Thanks