MacBook boot not working, fans active

Hi all,

I have an old broken MacBook here. When I hold down the power button I do here the fans starting to turn, the hard disk unlock (or at least some sounds) like it's booting up but the screen stays black, I cant eject a disk, the shift key light can't be turned on and no boot sounds is heard. After 10 seconds the sounds die down and goes to a minimal fan speed like it's on sleep.

I've tried to boot it while holding shift and also the PRAM reset (option, cmd, p and r).

Any ideas what could fix this? Is it a common problem? Something seems to work still so I have hopes of fixing it.

Thanks!