I would venture to guess that you've wired up the IPAC wrong. The PC sees the IPAC as a keyboard. If you have your wiring shorted out, then the PC is going to start thinking you're sending keypresses too fast. The beeping is the PC basically saying "enough already!. If I remember my basic PC design, it's when the keyboard buffer is being filled faster than the PC can process it. When you exceed the buffer, the PC gives the appearance of hanging when in actuallity it's trying to process the key presses.
In short (excuse the pun) double check your wiring and make sure it's right.