Does a company have to pay over time if you are currently on salary and working more then 40 hrs a week?

Salary is a payment method. The question is whether you are exempt or non-exempt from the overtime provisions of the Fair Labor Standards Act.

http://www.dol.gov/esa/whd/flsa/

If you are an exempt employee, then barring a bona fide contract that specifically says otherwise there are no circumstances whatsoever in which you are legally entitled to overtime, even if you work 168 hours per week. On the other hand, the circumstances under which your salary can be docked for time you do not work are extremely limited.

If you are a non-exempt employee, then even if you are paid a salary for 40 hours a week and under, you still have to be paid overtime when it is worked. However, outside of a few state-specific exceptions for voting and jury duty, you never have to be paid when you do not work.