I have been Litecoin mining with an Asus HD7850, getting around 300KH/second. Suddenly it won't go above 16KH/second for same config file. It is also slower to respond to window movements on the scrreen. I suspect that I've burned out some but not all memory and the drivers are somehow working around it without complaining. Is that possible, and are there any hardware diagnostic programs available for Radeon HD series? I have Googled and I don't see any diagostics available.