Computercraft lags while holding keys down when my keyboard is plugged into PS/2

I have a mechanicial keyboard that came with a USB to PS/2 adapter. Before, when it was plugged into USB, Computercraft would not lag when holding down a key. Now, it lags horrablely and causes huge input lag. It seems when I hold down a key on my keyboard, it registers it very fast rather than slow. So holding down A for a second would be like aaaaaaaaaaaaaa rather than aaaaaa.
I'm not plugging back into USB's .5ms delay, and I can't switch without restarting.
I'm running Windows 8.1, is there a program I could run to temporaily slow the spamming of keys while behing held down?
edit:

You have a windows 8 compatible computer that has PS/2 ports? I would not have thought such a thing existed…

1 PS/2 port–what $100+ motherboard wouldn't include one?
I built my computer myself by the way. Funny thing, I was originally running it a Hackintosh, then switched it over to windows. So I've switched OSes without switiching computers!
I should also say my computer is far from old, running at
3.4GHZ quad-core i5, 8GB RAM, Nvidia GTX 760 @ 1.2GHz w/ 2GB 8GHz RAM