sounds lijke one of two ideas might help. If the old game is written in VGA or worse EGA then on a big screen you may have to downgrade the scereen to VGA por EGA and lose quality to get it yto fil the screen.
However you say it also happens at startup. often at start up the basic screen driver VGA is used and then later in ther start up proces it changes to what yhe video drivers / video board can cope with. It could be that the settings on the viceo board are forcing the VGA startup.
M