Okay, so you understand how to rework solder. Then you should also be able to reseat the heatsink.
You should know that the MOSFET area of the MB has probably been affected if you took an electrical hit and it doesnt matter what card you put in there it will either be affected already or will become affected later. Furthermore if the PSU has been affected already then any new device you add will have the same problem migrate in over time.
Your suggestion about the heat sink was appreciated. However, you may have missed my follow-up question. If the heat sink is the issue, wouldn't you expect the video card to display correctly when Windows has just loaded (when the temperature is still climbing through 30 degrees C as indicated by the "ATI Tool" utility), and then to exhibit the display anomalies only later, when it stabilizes around 52 degrees C?
Instead of the above, the card displays the symptoms shown in the posted image, from the first appearance of the Windows log-in screen.
BTW, I was only guessing that my system was hit by a power surge during the night; it may not have been. It’s just that it “worked” the night before, and didn’t in the morning.
MH