Update your post to include full system hardware specs and OS information.
Include PSU: make, model, wattage, age, condition?
Disk drive(s): make, model, capacity, how full?
What all did you do when the GPU was cleaned? How was the interior cleaned?
Maybe something was bumped loose.
Double-check that all cards, connectors, RAM, and jumpers are fully and firmly seated.
Look for signs of damage: bare conductor showing, melted insulation, pinched or kinked wires. blackened or browned components and/or surfaces.