Replaced battery. Black screen. Fans running.

Hello, I really hope you can help me. I start a new job next monday and need this macbook working or I might lose the job on day one.

I ordered a new battery for my macbook and replaced it today. I took great care with everything and followed the tutorial step by step.

Now I have the following problem:

I turn on the Macbook. The fans start running and I hear the start up chime. The keyboard light blinks once real quick but only on the left side. The screen stays black. The touchscreen and everything else dont show either.

After a few minutes when the fans have ran quite loud, it shuts off.

I tried taking off the battery and purely running it in power but it did the exact same thing.

i tried resetting smc and all the key combinations advised but literally nothing works.

I triple checked the connections and all is connected well….

This morning before changing the battery all was fine… I really have no money for a new macbook or even cheap laptop atm.

Can anyone please help?