Airport Extreme Card


I have tried recently to install an airport extreme card in my 20 month old powermac g4. I am running on osx 10.2.3. I know I have installed the card correctly as I rang the apple help line and they talked me through it, however when I went to re-boot after installation I got a grey screen telling me (in several languages) to re-start my computer by holding doen the power key. When I do this I end up with exactly the same message again. My instruction guide and spec tell me that the mac is configured for airport extreme, is this an age issue with my mac or the operating system??? Please help!!