guix:
Did I just waste my money because an IDE cable can't handle the 5V required by the display (3.3V required by the backlight) ? I measured resistance between the 2 ends of some wires, multimeter show ~0.8 Ohms for each.
While IDE drives get their power by other means, I'm sure your ribbon should be capable of running a TFT, particularly over such a short distance. If your ribbon came with hardware each end, you have solved the biggest problem - the termination of so many tiny wires. But I don't understand the male/female bit. I thought all IDE ribbon was female each end. I therefore don't think you are telling us the whole story, and what you are not telling us about could be where your problem lies.
Failing that, it could be a missing solder joint on a prototyping shield. I had one of those lately.