I just got back from holidays and I can't boot up my intel imac. I have run Apple Hardware test with a pass, but disc utility does not see the HD. When I press the power button, I get a clicking sound every second or two. I hold down option and get nothing unless I have the DVD in the drive. I have tried to mount in target mode and get nothing. Is there any other tests I should run before taking it into the repair shop? Are there any programs I can run to try and get back data?