As it was a C64 emulator it almost certainly will have tried to change your screen settings to enable the games to run. Flat screens have a 'native' pixel size and don't like running at any other setting. Right click somewhere in a blank area of the screen and choose Properties, Settings. Make sure it is set to 1024 x 768 and 32 bit colour.
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.