Try your other card, if you still have it. If not, try re seeding your current card. I wouldn't think a hardware accelerated program would ruin a card, but it's possible with a card under a lot of stress, although quite small. If you can't get it to work, it should be under warranty if it's a couple weeks old.
In the future, you should disable flash hardware acceleration by right clicking any flash object and going to settings.
This, try another card on the computer or/and try the 5870 in another computer. This way you will be sure where the problem is.