Last question first, as we need to know what operating system that the Mac is using.
If you are not sure, click the Apple icon in the upper left corner of the screen, then click About This Mac, and post back with the OS X Version number that you see there.
Two possible solutions on the power cord
ORIGINAL OEM APPLE AIRPORT EXTREME BASE STATION POWER SUPPLY AC ADAPTER A1202 if you want a white power supply and white power cord to match up with the Apple device
AC adapter for Apple AirPort A1034 Extreme B... if you don't care what color the supply and cord might be
If you don't already have a Setup Guide.....look here:
I think your Airport Extreme came with the sotware on a disc. If you don't have the disc this thread may help download and install the software.
The post by Tesserax, forum expert explains in detail. Good luck!