Well then - the thing that has changed is your monitor hardware.
It should have come with a set of drivers for it. Did you install those, or just plug it in?. If you did not, then doing so may help.
And it may well be that your new monitor itself does not like 1024 mode, or if it supports 1024x768, then it may not like lowly 256 colour as the manufacturer has decided that's so totally obsolete these days. In which case - go to windowed mode at desktop resolution, and resize the monitor to your eye's liking and that does not skew the graphics too much.
Andy
(PS - eye ops no fun, had a series of 3 injections myself, then another, now waiting to hear if more needed..
)