http://www.cathaypacific.com/cpa/en_...tomerrelations

I'm sorry to hear that your IFE didn't work. Did you ask/ making complain to the flight manager on the plane. (usually the manager has the power to issue compensation)

Since your trip was already over, you can however write to the customer relation thru the link about, and I would also send a letter to them to show that you are loyal customer and hope them will fix that IFE in the future. and tell them what a disappointment once you found out the IFE is not working. (Something like that) I think they will give you some kind of offer for your next trip.

Wish you best of luck.