Chosen Solution
I recently took apart my macbook pro late 2011 to redo the thermal paste. When I put everything back together it booted up perfectly fine but refused to take in power (running on the battery before I changed stuff up). I have tried cleaning the area around the CPU in case thermal paste fell on it and have plug stuff back in over and over (except the keyboard ribbon cable because that was a pain). When I plug it in though the LED light is EXTREMELY dim, but there if you turn off the lights and look close. But no matter how long I leave it, it’s still dead (it died of power loss). Whats going on?
Ouch! Some how you managed to damage the logic board. You could have encountered ESD damage for static electricity discharge. Do you have an ESD mat and followed good ESD practices? The other risk is while working on the logic board you snapped off a SMD component as you were fighting with the heat sink screws. Lastly, your luck ran out either the charger was a knockoff or the cord was damaged so power ran down the center pin in the MagSafe connectors damaging the SMC logic on your logic board. You’ll need to inspect the logic board for physical damage hopefully you can see it. If not you’ll either need to find someone with the deeper skills to fix your logic board or just replace it.
