Happened to my wife on a recent HKG > LHR flight in CW. The crew were very apologetic, tried to reset the IFE for her seat twice but it unfortunately made no difference. They did offer to move her to another seat but the cabin was fairly rammed so it would've meant a seat no where near myself. It's a night flight and she had her e-reader so wasn't overly fussed.

On reaching LHR had a few hours before our next flight (ex-EU trip) so I just filled out the online form on her behalf and politely suggested she should be due some recompense, for example some Avios, as she had not received the full service expected or paid for.

Only a few days later 9,000 Avios were credited to her BAEC account. No fuss, no drama, no chasing for weeks or months. Top marks for BA IMO.

I do think it helped that I was factual, polite, and suggested what I thought would be a mutually beneficial, quick and easy resolution.