So in some three months of BitCoin mining with a Radeon 5770 in a dusty environment, there was eventual failure. From boot time with the computer at room temperature the graphics card would mine for about 10 to 20 minutes before the computer would shut off (and run up to 93C+). This computer previously had some issues with shutting off prior to installing this card, which was also prior to installing Windows XP Professional 32 bit over the Windows Vista which got rid of that issue. Anyway, I decided first to take a look at the inside of the graphics card to determine if there was any buildup of dust. My assumption of the dust was correct.
To open up the XFX RADEON HD 5770, every screw on the board needed to be removed, and the four screws for the heat sink needed to be loosened. After that the plastic case came right off. Carefully disconnect the fan lead from the board and the two halves can be separated.
I wiped off the old thermal compound from the chip and the heat sink. Then I unscrewed the four screws from the heat sink. There was quite a bit of build up of dust in one side once I pulled it out. I cleaned the fan up and blew the rest of the card out with compressed air. Then I replaced the thermal grease and put it back together. Now it mines again. 🙂