Perdon the intrumision but...

[Strongwolf]

Where can I find my Network security key?

[danrok]

Network security key for what? A mobile phone?

[booman]

is that the same as a MAC address?

[Aedan]

WiFi network?

[booman]

oh yeah, he probably means the Wifi key or Access Point key.
You have to login to your router or access point to reset the key.

1. Start by connecting a computer to the ethernet port
2. Open you internet browser
3. type the IP address of the router/ap in the address bar
4. most Routers should look like this: 192.168.1.1 or 192.168.11.1 or 192.168.0.1
5. When you connect you will be presented with a web interface
6. Hopefully there is a password and you know it. Chances are there isn't a password
7. Try login: admin pass: leave blank
8. Then look for the Wifi Key
9. Update the key, apply changes then try to connect with your laptop/phone

[Strongwolf]

A little late, but thanks a lot Booman.