Check the VGA card and search for some Oil like gel , probably its will leak from the thermal pad, you might not going to be able to see it without removing the cooling block and fans. If dust stuck into that gel , it might become conductive and can cause some trouble. If you see anything like this , just remove the cooling fans , backplate, and clean the circuit board .
For cleaning you can use any kind of Non-conductive, Zero Residue Contact Cleaner.
When I'm doing a cleaning like this, i always "baking the circuit board for 15 minutes on around 70-75C, in a Convection Oven with air circulation , just to stay in the safe side
What temperature you card is running during mining ?