To expand on Technostalgic, you can test your rollover of your keyboard with the following webpage and following the examples
http://gadzikowski.com/nkeyrollover.html
A lot of laptop keyboards and cheap keyboard have 2 key rollover – meaning you can only guarantee 2 keys being pressed at once. This makes certain games unplayable. If that’s the issue you’d have to either use a different keyboard or a controller.