doesn't display(totally black ) after changed fan

I bought a fan from ebay but it is not original. Then i disconnected the battery, removed the fan, connected battery again.(followed ifixit guidance ) When it started, fan, keyboard worked,while the screen doesn't display anything and Apple logo didn't light.

And I went to Apple store, they told me the logic is damaged, I need to pay for 280dollars.

So whats the cause of this problem?