I just finished debugging a FX2 board design and thought I would proactively post the solution to a problem that may bite other people.
The FX2 has a pin called "reserved". The board designer left it floating instead of grounding it as per the FX2 design doc. Since it's called "reserved", it was easy to miss in design reviews - the name implies it should be left open.
The error prevented the FX2 from coming alive. Windows noticed a device had been plugged in, but complained about an unrecognized device. While debugging, I notice the CLKOUT pin was static even though the crystal was clearly oscillating. The manual states that CLKOUT should operate even while reset is asserted, so this was a good hint that it was not a USB problem but some design problem.
I connected "reverved" to ground and the FX2 started working properly and Windows was happy.
I hope this can save someone some time!
John Providenza