Seems odd that the GPU itself would die because you cleaned it!!
I would check the power plugs especially on the GPU:
Are the pins burnt (blue)? If so are the plug pins loose?
What is the solder joints on the board like? (plug pins)
Do you have any electronic contact cleaner (spray can)? This is an essential for overhauling PC's and other electronic equipment.
Did you disturb any of the heatsinks? You may have to take them apart, clean and reapply thermal paste.
If the GPU is fine it could be a dry joint in the power supply that needs re-soldering.
