I recently fixed RAM problem and wanted wipe the HD clean and re-install the OS. After re-installing, the system will not detect the HD and will only boot from the CD. The HD icon will not appear on the desktop, start up menu, or the disk first aid window. I have swapped out the HD, but still have the same problem. Help.

The phrases you should be aware of: "I recently fixed RAM problem" & "After re-installing" & "I have swapped out the HD" suggest the three variables that you should investigate. Did you use the machine for some time after 'fixing' (HOW?) your ram problem to assure the 'fix' worked? Did you re-install the OS properly, running disk first aid, updating the drivers, etc? Did you set the jumpers on the new HD correctly and secure the ribbon and power cables? Reverse gears and check things out. Incidentally, there were a few firmware updates for the earlier iMacs you may want to look into and install. This may be part of your dilemma. From hence forth try one 'fix' at a time. Do too many things in rapid succession and your variables increase greatly in the event of a mishap. I speak from experience, as I have been in similar situations. You are in a large boat full of comrades on this type of problem.