I hope you didn't ACTUALLY blow on it. Breath has MOISTURE. That's what canned air is for, and it's usually much more effective.

hopefully not compressed air, it creates static and that frys electronics

I am betting the problem was not the air blown on the processor heat sink but some stray piece of hardware like a loose screw that shorted out something on the motherboard. Sometimes people are sloppy with the hardware. I am an electronic engineer and I never saw anything actually damaged by blowing air on it unless it moved a loose piece of metallic hardware into a place where it shorted out something. An even more probable failure mode is a loose connection or a plug in component not properly seated that got jiggled while trying to blow out the dust. Make sure the memory modules are properly seated and the connectors and plug in modules are fully and properly seated. Of course if you smelled something smoke and burn then game over unless you are proficient at electronics - Take it to someone who is proficient.

did you try removing the CMOS battery having the BIOS reset that way and then putting the GPU back in place?