Do your pro-minis have an LED on pin13 ? (On the official board, this seems to usually be near the reset switch. Other versions I see with two LEDs, it'd be the one that ISN'T the power-on LED)
Does it flash a few times, quickly, when you hit the reset button? If not, it implies that there is no bootloader present.
If so, does it do the same flashing when you hit the upload button in the IDE? If not, it implies that there is something wrong with the auto-reset circuitry.