Here is the original item:
Smiling with satisfaction
(A) Michelle typed
the last sentence of her research paper. Then a bolt of lightning crashed
nearby,
(B) extinguishing
the electricity (C)
and making poor Michelle wish that she had invested in a surge protector.
You wanted to do this:
Smiling with satisfaction Michelle typed the last sentence of her research
paper. Then a bolt of lightning crashed nearby. Extinguishing
the electricity and making poor Michelle wish that she had invested in a
surge protector.
A period after nearby makes a fragment. Extinguishing the electricity ... is a participle phrase, which cannot stand alone as a complete sentence.
You might want to review the rules.