ML150 G6 CPU upgrade - NO BIOS POST

Folks,

I want to upgrade my ML150 G6 (which runs just fine as is with Linux Distro) from a E5502 to a E5506.  The E5506 is taken from a working ML330 G6 so is confirmed as without issue.

Problem I have is that when install the E5506 the server will not POST.  The fan test completes ok - I just get nothing on the screen.

I have tried different memory modules and combinations but no change. I have also reset the BIOS - again no change.  Current BIOS on the server is 021 dated 18th Jan 2011.

TIA - Any assistance would be very much appreciated.