Final answer:
The sentence is punctuated correctly with a present participle phrase followed by a main clause.
Step-by-step explanation:
The sentence 'Checking the computer system, Steve discovered a virus.' is punctuated correctly. The sentence starts with a present participle phrase, 'Checking the computer system', followed by a comma to separate it from the main clause which is 'Steve discovered a virus'. This sentence structure indicates that Steve discovered a virus while checking the computer system.
Learn more about Punctuation in English sentences