I ran into the same FaceTime problem with my iMac. I attempted to connect with my mother on her iMac, and it would just ring and never connect. However, I was able to fix it without turning off my firewall. Here is how:
1. Scan through the Apple article that talks about using port forwarding to fix firewall issues with FaceTime (http://support.apple.com/kb/HT4245).
2. If you are on a wireless network, open AirPort Utility. Make sure your wireless router is showing up, and then select 'Manual Setup' at the bottom of the AirPort Utility screen.
3. Icons will then appear at the top of the AirPort Utility screen. Click on 'Internet' icon. The screen then automatically defaults to the 'Internet Connection' tab. However, you want to work on the 'NAT' tab, so click on that one.
4. Under the 'NAT' tab, you will see 'Enable NAT Port Mapping Protocol'. Make sure this is checked off and then click on the 'Configure Port Mappings' button.
5. Once you click on the button, you will see a listing of already defined port mappings. I had never 'port mapped', so the listing was empty for me. At this point, just click on the '+' sign to add your new port mapping.
6. You will see the option to 'Choose a service'. You don't need to bother with this right now. However, make sure you type the following into the blank boxes on your screen:
Public UDP Port(s): 3478-3497, 16384-16387, 16393-16402
Public TCP Port(s): 443, 5223
Private IP Address: Do not type anything in this box. It should already contain your personal IP address.
Private UDP Port(s): 3478-3497, 16384-16387, 16393-16402
Private TCP Port(s): 443, 5223
7. Click on 'Continue'.
8. It will ask you for a description of the new port mapping. I just typed in 'FaceTime' and left everything else in the screen blank. Click on 'Done' and you should be all set.
If the person you are attempting to contact through FaceTime is also on a Mac, he may need to also follow these steps.
Hope this helps.