Welcome to the forum!
If you really really want that sword in the stone and stop the ghost .. there is a cheat:
Spoiler: After you have taken the sword and killed the ghost, make sure the sword is in your inventory - save, and then drag out the sword of your inventory - and keep the mouse botton down while doing so and load (Ctrl + l) and you should have 2 swords. Put one of them back into the stone and the ghost is killing no more.
