sorry, to ask here, but what actually happened to your video cards: fans problems or you burned them? If burned, what average mining temperature was?
A few just don't work, but a lot can still mine btc but don't work for anything else really. A few number of the cards will still mine ltc. I'm pretty sure the vrm, memory is the most common failure. It's hard to tell anything is wrong until you run some benchmarks one card at a time.
I try to run them in the low 60's if possible. If you run them at 70-80 it doesn't take long before the cards are just not stable anymore.
If anyone needs some half functional 5970's, 5870's I have plenty.