Geforce 9800GT

Hi, I bought an 9800gt which got overheated so, I opened it and cleaned it . But after closing it when I tested it didn't power on. Any help plz???

I have an HP ENVY 15 laptop with Windows 8.1 that I've been using for two years (forced upgrade to 8.1 sometime during then), and in the past few months, it started doing this. So, for quite a few months now, when I am playing Dota 2 or watching youtube videos, my computer will suddenly lag...