I cannot hear the HD spinning as I've previously installed an SSD

I'm having a similar problem. I cannot hear the HD spinning as I've previously installed an SSD.

Mid 2011 iMac 27 3.4

My symptoms are:

1). Generally boots only on second or third press of power button

2). At boot process the 2nd never lights but all of the fans spring slowly then moving up to what appears to be full speed.

I recently upgraded to a k5100 which was successfully installed and operated without issue for several weeks.

I replaced the power supply last week and today replaced the logic board - problem remains.

One other strange thing I was unable to diagnose - the iMac was booting the fist three logic board LEDs but not the 4th. I've switch the screen with another 27 I have and it worked without issue.

I'm not sure where to go next with this issue -- if anyone has advice I'd really appreciate it.