Isn't working / doesn't work

Hi,
I am taking a faulty gadget back to the store and walk up to a clerk. I say:

"I am sorry, but this thing isn't working."
"I am sorry, but this thing doesn't work."

My English instructor told me that in this case I can use either tense. The present continuous emphasizes that the condition is temporary ("right very now"), but in this case the two are interchangeable and I can say either one. Is that correct?

Thanks,
Maria