I replaced the keyboard and now I got black screen and key board not respoding?

Like the title suggest. I replaced the keyboard c cover as one key doesn't work anymore. The laptop turns on but screen doesn't come on and keyboard is unresponsive apart from back light. I even switched back to old keyboard still same issue. IdeaPad Gaming 3 16ARH7

Things I have tried.

1. Power button hard reset.
2. Turning the laptop on online on AC without battery and using external keyboard.

Things I am waiting to try.

1: repaste the thermal paste as the last time I tried to check before I tried to turn on after replacing keyboard. It came on fan ran very high and then it turned off. So, i thought it might need replacing as its been 2.5 years since i have bought it and used it afew hours everyday.

2: I have disconnected all the batteries including cmos and hopefully it will discharge any residual charge(been 36+hrs).

Is there anything else that you guys recommend I should do if above steps don't work?