Laptop sometimes won't start unless charger is connected?

It's a Dell laptop, I got it about 2 years ago. I've had problems with the harddrive before, so my memory before had to be wiped. The screen hinges are kind of beat up and battered, and the light indicating my laptop's on sometimes doesn't turn on unless I put the screen in a certain angle. Occassionally my laptop won't start up at all unless I plug it in. What could be the problem? Is my laptop basically just so beat up that it's having these problems?