MacBook Pro 2009 won't turn on

Hi,

My macbook was overheating so much that I decided to re-apply thermal paste. I had to take the logic board out, but when I reassembled it it didn’t turn on. I thought it was power issue because when I connected the adapter, the battery indicators started flickering, so I bought a new battery.

Oh, BTW, my old battery was dead so I didn’t have it connected and it worked just fine before.

Today new battery finally came so I replaced it, it came 50% charged so i fully charged it (it took about an hour) and then tried to turn macbook on. It didn’t work. Then I tried to turn it on with charger connected and it still didn’t work. What should I do?

Thank you

Edit: I forgot to mention, this happened to me one time before, but I just waited for like 30 minutes and it turned on. Now it’s been dead for like a month.