It sure sounds like the card is dead or near dead. Since you got it for free and it's probably unuseable anyway, you might try this experiment. It is NOT intended to turn your card into a good one. It is simply a technical exercise to see if the card is really defective and if the defect is heat-related.
Put it in the fridge for, say, half an hour. Then fit it into your computer quickly and turn it on (before it has had time to warm up to room temperature), and see if it works for a short while.
If it doesn't, try the opposite. Before turning the computer on, blow on the card briefly with a hair dryer - say 3 or 4 seconds. Then turn on the computer.