Starts to boot and then shuts down shortly afterwards.

I recently replaced the fan on my MBP. I purchased a used fan from ifixit and swapped that because mine was REALLY noisy. Then about a week or so later this started to happen. The blue light on the front still blinks slowly, I have to force shutdown the machine, but the screen goes blank and nothing happens. No noises from holding buttons or anything.

I've tried all of the different resets I can find.

I've swapped in a different HDD.

I have no idea what else could be causing this.