just got a used airport base station. Set it up and getting wif signal. when I try to hook up on a computer it asks for a security key. where can I locate key?

I would suggest that you perform a "factory default" reset on your newly acquired AirPort Base Station. This should erase any existing passwords that were established by the previous owner.

If you mean the hexidecimal equivalent of the alphanumeric password, then you can find this via the AirPort Utility, as follows:

• AirPort Utility > Select the AirPort > Manual Setup
• On the AirPort Utility's menubar select Base Station > Equivalent Network Password

If you did a factory reset, then you should be able to configure your Airport Base Station...

Otherwise if you did not did it following the acurate steps, then you had failed on the reset and thats why it is still asking you for a security key...