I only borrowed this game a long time ago so cant be sure of details but somewhere there is a 3 holder candlestick thingy floating about,if you light that then follow it the caretaker ghost will take you where you need to go,I think!
First dont try and kill the ghosts as they just keep reinventing themselves, just run past. Go to telephone room on the 1st floor 1st call from toad, tell him you are Luigi and that will save the game. 2nd call from prof. tells you the key you need is with unlce grimmly then clear the room of ghosts, you can find grimmly on the 2nd floor in the closet.To kill grimmly wait untill he raises his hands and hit him with a beam of light and pull him in with the vac. you will now get the key so go to the basement and restore the elctricity by throwing the trip sw.