Which of the following sentences correctly uses a semicolon?

1 someone totally messed up my room; my sister looked very guilty.
2 i tried to move the desk to find my fallen paper; but it was too heavy.
3 ellen changed the light bulbs in the lamps; washed the car; walked the dog; and swept the garage.
4 it was hard to find our way through the house; for the lights were dimmed and the sun was down.