MacBook won't boot on MagSafe

Hey !

I've recently replaced the LCD panel and the battery on my A1229 MacBook Pro. I used it without the battery for months and since the replacement i have two problems :

- when i try to boot with the MagSafe plugged (battery or not) i get the grey screen saying "you need to restart your computer" - on battery only it boots without problems

- when i plug the MagSafe while the computer is on, the screen starts flashing after a while and then it freezes...

The battery charges normally when I plug the adapter.

Any ideas...?

Thank you for your help !