iMac 20in makes three beeps and fails to boot?
I have just changed the hard drive on my previously working 20in Intel iMac. The drive was pre-formatted and loaded with Mountain Lion using an external dock. The computer functions when fire-wired to another iMac, showing the doners desktop. Now I hear three intermittant beeps when pressing the start button on the 20in iMac. The screen remains dark. (It is assembled, but I have not fitted the aluminium front bezel or the glass yet). It does not respond to any keyboard commands. The memory moduls have been re-inserted firmly. Help please?
iMac, OS X Mountain Lion (10.8.5)