Compaq N800C laptop doesnt start!!!!!!!!!!!

Hello,
My problem is that a computer that had a bad card slot that i fixed. after i put all the screws in, and tried turning it on, all it does is make some regular noises like always but the light that has the battery symbol under it justs blinks for a little bit and stops. Also, the screen doesnt light up or do anything. please help me!!!!!!!!!!!!!!!!!!!