Does not boot, battery runs out in a few hours

My Brothers gave me his MacBook Pro to take a look at it. The display was acting up, showing just colours, no image. I thought it was a loose connection, so I opened the thing up, unplugged the battery, checked the connection and closed it back up.

Now the thing is completely dead... Wel... Not completely. The MagSafe led burns when I connect it, end the battery charges, if I may trust the battery indicators. Apart from that, it does nothing. I also noticed that, although the machine does not boot, the battery runs out in a few hours after having charged completely.

I tried the SMC reset ( it makes the led change from orange to green, and back again), the main board reset, ...

Nothing. If you guys could help me out, it'd be great, since this my brothers MBP and it sucks that I kinda broke it...

Thanks,

Sam

Btw: it's a 13" MBP model n° A1278