Thanks to both theducks and kovidgoyal for your quick responses.
I am running on Window 7 64 bit so that update problem was not the solution for me but I downloaded the latest version and reinstalled it anyway just to be sure.
As kovidgoyal says ... there was a button that I had entirely missed ... the top right yellow button with a scroll on it .... I really am an idiot sometimes
Which brings me to another question: Is it possible to modify the scrolling factor so that one click of the wheel advances by one line only?
Note: this is the Windows 7 mouse setting in effect right now and this setting works in most other text based programs but not in calibre for some reason.
The reason for this requirement is that I setup Calibre as a e-reader for some disabled people - who often have to use extremely large type just to be able to see the text clearly. When the type is large you only get a few lines on the screen but a scroll click jumps too far ahead.