They gave me an old iMac and I bought a keyboard for it and I have a pro mouse(the clear ones). At first I read that if the question mark pops up to ensure the mouse and keyboard are plug in. Now I'm thinking my pro mouse is not compatible with my old imac. I also don't know how to reinstall the OS because I don't have a system disk. What should I do to get this thing going? I think it has mac os 8 or maybe 9. I'm also a complete newbie to macs. Thanks.