Are you sure you have the ribbon on the new one the right way around? Have
you replaced the ribbon? How do you know the new one is broken? Connecting
the ribbon the wrong way around won't kill a floppy, but it will render it
useless until you put it right. Yes, the floppy controller on the mainboard
could be broken.
A reverse cable won't damage the floppy drive, but it can damage the
floppy disk in that drive.
Since one side of the connector has all the pins to ground, and all or
most of the control lines on the drive are active low, reversing the
cable can do things like turn on the motor, turn on the drive
select, turn on write, and then it starts erasing what's underneath it.
So it's best to do testing with a floppy disk one doesn't care about.
It is pretty easy to pull the connector out at the motherboard without
realizing it, I've done that when trying to do something else. Yes,
it is more likely the connector has pulled out somewhere than that
a fatal hardware fault has developed.
Michael