Having same issue with Icewind Dale. I have fix packs and unfinished business for BG2 also tried widescreen mod. No matter what resolution I try, the viewing screen is just a small square in the middle with black all around. I've played both IWD and BG2 before and never had this issue. Using Win10.

You need to look at scaling options in your video card software (CCC or Nvidia Control Panel)
maybe perform scaling on GPU instead of display.
try override scaling options set by games

with Nvidia they are under Adjust desktop size & position.

I have an intel graphics card HD2000. I've never adjusted anything since I bought the computer and I was playing these games a few months ago but I uninstalled them and now I have this issue.

Was this before you changed your operating system?
Intel don't make any win 10 drivers for their graphics chips.
If your drivers are older than the current 15.28.24.64.4229 intel drivers, you could try those

Things to try.

Run BGConfig & disable 3D Acceleration

Press Ctrl + Alt + F11 to toggle scaling options.

Well, turning off 3D acceleration seemed to have done the trick.
Thanks!!