Just quickly looked through forums and couldn't find anything similar to my problem. When I start up my imac, the screen stays white for around 20 seconds and then a flashing earth appears. I think if I wait a while it eventually comes on, but I dont know if this is the case, I will look into it further but if anyone can give any advice for now, that would be great. I'll keep you updated.
Cheers.
Cheers.