Whew, troubleshooting issues like this can be a nightmare. Needless to say you can look at a few items to make sure it's not something obvious. Heat does seems to be a common culprit for the kind of issue you're seeing but it can also be hardware failure. Had things worked on 7068 before the later drivers? What about playing DVD's? Did you install a codec pack? It could be a codec problem. You can try looking at the file using GSpot's Codec Information Applicance
to make sure you have the proper codec installed.
Reseat your RAM. I know that might sound goofy but one some sticks and board combos this can be a little sensitive. Run the memory test, make sure there isn't anything silly going on there.
It seemed like to me the resource allocation was different from version to version (I used 7000, 7057, 7077 briefly and now 7100) and you might be experiencing a conflict with another device. Check the Conflicts/Sharing under Hardware Resources. You will most likely see a number of motherboard resources sharing but if there is another PCI device conflicting try removing it to another slot.
Failing power supplies or ones that don't provide clean/consistent power on the 12V legs (or others) can cause issues as well. Are you using the adapter to convert the molex power connectors to the 8-pin/6-pin connectors? If so most if not all manufacturers strongly recommend you upgrade your power supply to one that supports those connections natively as the GTX 280 is a powerful card with high power requirement. If you're using EVGA you should download the EVGA Precision application if you haven't already which will allow you to control the fan speed, etc.
You could also try upgrading or clean installing RC1, it's out now for CPP.