Fps rate being abysmal in some games, while others run smoothly.

This problem so far happened to The King of Fighters 98 UM, 2002 UM and 2000.

This is specially weird, since King of Fighters XI seens to run just fine. Other games that run completely okay are Gundam vs Zeta Gundam, Federation vs Zeon, The Last Blade 1 and Auto Modellista.

I tried running Kof 2000 with software renderer, but that hasn't resolved the issue, but I'm also not very tech savvy, so I don't really understand well how the pc specifications may be affecting these games.