Take a look at the original sentence again:
For two weeks, Todd refused to go to his accounting class because Professor
Gastineau would not allow students to wear hats in
class, under no circumstance would Todd
allow anyone to see the butcher job his stylist had done to his hair.
You wanted to fix it this way:
For two weeks, Todd refused to go to his accounting class because Professor
Gastineau would not allow students to wear hats in
class under no circumstance would Todd allow
anyone to see the butcher job his stylist had done to his hair.
To delete the comma between class and under would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two complete sentences joined with no punctuation whatsoever. For two weeks, Todd refused ... begins the first complete sentence. Under no circumstance would Todd allow ... starts the second complete sentence. The spot between class and under needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.
Go back to the sentence to try again.