없어요 없죠. (죠 is short for "-지요")
I think you know their meanings. They normally means 'do(es) not have or there is(are) not'.
What I'd like to emphasize is that '없죠' is used positively.
Let me give you examples,
A : Do you have a car?
B : 없어요.
A : Does your car have any PROBLEMS?
B : 없죠 (OF COURSE NOT. It does NOT) The fact is positve even though the answer was negative.
없어요. (no, it does not)
I want to explain more in detail, but my english is limited.
Maybe someone who speaks better English or Chinese will help you.