Power Antenna
If its the motor, what is the part number?
With the car off, have you tried to gently pull it up or push it down? If it eventually "catches" and goes down, then it may just need to be lubed up. Otherwise, it may be time for replacement. If the car is still under warranty, then this may be covered.
PN: 10402859
Here is a site on how to install it. The site is about how to install it in a Camaro, which didnt some with a power antenna stock, but it should still be of some help.
http://www.blackcamaro.com/antenna.htm
If its the motor, what is the part number?

Easy part to replace if you want to go that route. Only $70 at gmpartsdirect.




