I have an older Mac Pro that started showing strange green blocks and lines while playing back an online music video. In any case I thought it must be the Nvidia GeForce 8800GT card but thought I would try everything else first. I swapped RAM cards, replaced Hard Drive and tried reinstalling Snow Leopard. At this point i cannot get it to boot up from CD as I get the "shut down" message however I am able to boot up Windows which I installed via Bootcamp. Anybody have any thoughts?