I have a 2007 24" iMac with 4GB RAM and internal 320GB HD. A while ago the machine froze and then would not boot. When I run the Extended Apple Hardware Test I get the error "4HDD/11/40000004:SATA(0,0)". Is this more likely to be a problem with the HD or the logic board?
A quick web search for that error indicates that it is a hard drive error. Some have suggested being able to boot from the disk in either Safe Mode or Target Disk Mode from the system install disk, mainly to get needed content off before a complete failure if it hasn't happened yet. Either way, you need a new hard drive.