Once game finished it goes into the "High Score" screen.
A) How can I enter anything on this screen and B) how do I get back to the game ?
At the moment to exit the screen I am having to hit Windows button and then DOS box tab in task bar to bring up the high score screen in reduced size and the am able to close screen down. Then have to go through whole restarting of game again ! Surely there is a simpler way ?

When you get to the High Score screen just type your neme with keyboard.

You're only able to enter your name on the Hallowed Hall of Talent if you've done well enough to beat any of the High Scores there. It shouldn't be difficult to do so.

If you're anywhere in the game and you want to get back to the start screen, just hit Escape and that should get you there.