After several years of dependable service my IMac began to require a "warm-up" period before it would actually startup.
By this I mean that pushing the power "ON" button causes the power button to light amber. The fan comes on. Then one relay click followed by a second click happens and then no change. The light stays amber with no other sight or sound regardless of how long the IMac is left on.
If after some time, perhaps 20 minuets, I push the reset button with a paperclip or alternately pull the power cord and reconnect and then press the power button the IMac cycles on normally.
I have tried the following: changed the battery, disconnected all external cables, tried a CD startup disc, reset the pram, reseated all connectors on the cpu board and reseated the memory.
I suspect that there is some sort of thermal issue with the power supply board (thgough I do not know where this is exactly).
Replies gratefully accepted.