Kakero - thanks for the repsonse and possible answers!
Your right that I get very close and nothing and back away and nothing. I have a save with just one troll, and just tweak and reload and try and hit the guy! If I back away he uses his bow and close up, his club, I have tried step-time and realtime, and have swords and spells chosen so my party can attack close in and at distance and they do nothing in either case!
I have played around with the mouse settings in game, but the quandary is that my mouse works perfectly in the village! I can buy armour, talk to characters, set up characters, etc, which all involve mouse clicks! I have to click on one of the gates, after all, to get out of the village. It seems the problem is how the interface changes when you're outside the village and the way the cursor icons work.
I do not have another mouse, so that would be an extra spend, so i'll have to see if I can borrow one, but given my mouse works in general, and in the village specifically, I cannot believe it's that. It literally works okay in every other gamer I have - and has done for the last year!
I will continue to try to solve the problem, and welcome any ideas, however silly, so I thank you again for at least trying to help - and I am very grateful!