Here are the corrections for the sentences:

1. **furnitures** → **furniture**: "We found an interesting piece of furniture in that old house we bought."
2. **who ran** → This is correct as is. (No correction needed.)
3. **telling** → **told**: "The dentist gave me a check up and then told me I needed two fillings."
4. **was** → **is**: "Of the two lecturers, the first is by far the best, partly because the person who delivered it had such a dynamic style."
5. **neither are computers** → **nor are computers**: "According to many educators, television should not become a replacement for good teachers, nor are computers."

So, the revised sentences are:

1. We found an interesting piece of furniture in that old house we bought.
2. Graham Bell was once a teacher who ran a school for the deaf in Massachusetts.
3. The dentist gave me a check up and then told me I needed two fillings.
4. Of the two lecturers, the first is by far the best, partly because the person who delivered it had such a dynamic style.
5. According to many educators, television should not become a replacement for good teachers, nor are computers.