MacBook won't boot - no chime - black screen - fans on high rev

You may want to see whats going on with the thermal sensors & what the fan is doing. This is a good app to see them: TG Pro.

I haven't seen SMC get stuck on its own. But I have seen where I've needed to disconnect the battery to do a good hard reset can make the difference. Basically, disconnect the batter then hold the power button for a good 30 sec and reconnect the battery.

Sorry guy sounds like your logic board is damaged here. If you can't start the system but your USB ports are working then you have a deeper problem within the logic board.

Did you get your system wet? Have a liquid spill or sit your system down on a wet surface at some point? These are often the cause. As the corrosive nature of what was spilled could slowly eat your logic board or cause a short.

The other possibility is a power surge damaged your system.

Here's the IFIXIT guide you'll need to follow to replace your logic board: MacBook Pro 13" Unibody Mid 2012 Logic Board Replacement and here are your possible choices:

• MacBook Pro 13" Unibody (Mid 2012) 2.5 GHz Logic Board
• MacBook Pro 13" Unibody (Mid 2012) 2.9 GHz Logic Board

Oddly similar scenario with my MacBook Pro - no solution yet . . .

Okay, I came across this exchange after my 13” MacBook Pro went dead right in the middle of loading the OS. I had been using it all day without incident until it had become very laggy to to the point of being almost unresponsive. I was doing research and had a butt-load of open tabs in Safari I assumed were drawing hard on the resources. So. I pressed the start button and held it until the machine shut off, then rebooted. Everything appeared fine until we got to the part of start-up phase where I believe the graphics driver loads and takes over the job. The screen went black and then immediately blinked to a state where the bottom half was white and the top remained black with some intermittent white lines and artifacts where the white and dark parts met. To be clear, that is how it has always behaved at that part of the start-up. Normally, right after the screen flash to black and white within a split second apple the logo and progress indicator return and then the log-in screen appears. This time the screen flashed and remained dark. When I looked I realized it appeared to have completely shut off. So I pushed the power button again. The MacBook Pro chimed, began to load, and then same thing at exactly the same point, appeared to go dead. This time pressing the power resulted in no response. No keyboard lights, no chime, no fan… nada. I follow the instructions for every scenario I find online about the issue, no change. When I reset the SMC, the light on the power supply changes to green then back to amber indicating the SMC resets but still no action or response when pressing the power button. So just in case, I connected it to power and allowed it to charge all night. This morning - no change. The MacBook Pro USB ports charge when I plug into them and SMC responds to reset commands but the laptop still remains dead.

A couple of other detaIls: The magnetic power supply and connector are NOT OEM. And after charging all night, the light indicator on the power supply never indicates the battery charge is complete. This is a brand new OEM battery that only showed 53 cycles when I looked at the system report this past weekend.

My next steps are going to remove the bottom panel and disconnect the battery and fan cable to see if that makes a difference.