I get a white screen with the apple logo and the time icon spinning. it's a late '06 intel model.
Startup holding the Option key and see if your Macintosh HD is present and selectable as a startup volume?
Startup Manager: How to select a startup volume
If not, then dig out the original gray Tiger Install Disc 1 that came with your iMac and run the Extended Apple Hardware Test.
Intel-based Macs: Using Apple Hardware Test
Retrieving data ...