Problem with simultaneous notes

[Target]PPD
[x86 or x64]x64
[Windows　OS]Windows 8
[Content]I can't press the four notes (Δ, ◻, O and X) simultaneously, when I try, It appears as if I had not pressed the buttons. When there's 3 or 2 notes simultaneously there's no problem...
[error.log exists]no
[What you did before error]nothing, It happens since always
Sorry for bad english... I'm spanish...

This is your keyboard problem.
Your keyboard does not recognize simultaneous pushes more than 3 keys.
So you have to buy new one, or re-config to recognize simultaneous pushes more than 3 keys.

Maybe you can check here about simultaneous pushes of your keyboard.
http://www.gigahype.com/nkey-rollover-test-page/