Is there a way to get another Orb of Rebirth ? i´m Stuck in the Tower now because i have 0 Points in "Light" and cant harm anything

Just run that is what I did eventually you will come across rooms with spiders and them eventually the mages tower and you won't have to deal with the ghosts no more

If you got the Spirit of Light familiar, he can damage the ghosts (although you still need to see them). Other than that, you could grind a level and put one measly point into Light Magic.

Your best chance is to drop all your excess weapons in the bank so they can't be stolen, equip the one you use, equip a high physical resistance armor, unequip all your pets and just run through the 1 damage ghosts.