That's actually probably not an I-pac problem.
A motherboard has what's called "Beep-codes", a certain pattern of beeps indicates things. One beep may be "Ok", two beeps might be "Video card failure". You'd have to identify your motherboard and google it's beep-codes, identify what they're telling you, and then post back.
It's possible that the code is "Keyboard failure", but that doesn't necessarily means it's the Ipac, it could be a partial failure of the I/O that controls the PS2 port, and being tempremental about the Ipac.
So my approach would be:
Google and identify beep-code
Test Ipac on another computer if possible
That PS2 stuff won't work when the Ipac is plugged in tells me the I/O is failing on it's input, but that could be either then Ipac or the board.
I'm actually leaning towards the board, because if it were the Ipac, the board should throw up a "Keyboard failure" screen on boot.