iBook not booting

[Joel]

Hi,

I recently purchased a 128Mb iBook 500 g3 at a knock down price. Since
then I've added an AirPort card. I then decided to add more memory. I took
out the existing 64Mb and added a 512Mb stick and rebooted.

I got a flashing '?' which I unerstand indicates that the System Folder
can't be found... I've since discovered that I can bring up the System
Picker by pressing the "Option" key on startup and can bring up icons
showing the OSX system on my hard disk and on the install CD. But I can't
get any further... Pressing enter or the arrow key on screen causes both
icons to hide and then get redisplayed.

I've tried removing all the memory and the AirPort card and I can't see
anything that I've scratched or moved inside while doing so...

Is there anything else I can try to get this working...?

Thanks in advance...

Joel