Do Kingston memory cards have technology that prevents them from being used on unintended computers? I'm trying to use a Toshiba 4400SX 16 MB card on my Thinkpad, and it doesn't recognize the card.
No, not that I'm aware of. You may just have a stick that's incompatible with your Thinkpad (whether it's a speed issue or the density of chips or the total amount of memory).
You may have to look this up in a manual for your model because it may state the speed and density of memory you need!
The RAM cards that I have have markings on the back indicating what models the card is compatible with - I stretched the list a bit by using T4400C/SX cards on a T6600C, but the format/structure of the cards might be quite different for another manufacturer entirely. I've only dealt with Toshiba cards, myself.
It's a 755CD. I read about disabling parity in the manual, and I think I tried it. Disabling parity is config → memory → two flag-looking things next to an X, yes?