> For some reason, I can't press three buttons in an emulator
> at once.
This is not an emulator problem... it's a keyboard problem. Keyboards aren't designed with this kind of use in mind... they're not expecting you to hold several buttons at once... they're only expecting you to type one at a time. So pretty much... when you hold 3 keys... not all the info is getting to the computer... so there's no way the emu can know you're pressing those keys.
The best solution is to get a gamepad. Or preferably a PSX->USB adaptor or something of that sort. Controllers and gamepads
are designed for this use, so they won't have a problem.
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