I have a Dell V130, why is it that i cant press 2 keys at the same time (trying to do a super move)?

Iam playing Marvel VS Capcom and iam playing with RYU and iam trying to do the super move, and for some reason, when i push down forward and then the 2 punch buttons, it seems like the system wont let me do that, what is going on, is there a way to fix this in the keyboard settings.