I found it after stripping the card prior to baking, which was to be my last resort.
Was wondering if I could have moved it inadvertently whilst cleaning, because since then the card has prevented the PC from completing POST.
Noticed that on the base plate under the switch is stamped "1" & "2", it's currently on "2"
The card was working fine (for 2 years) before I decided to give it a quick clean, without dissembling - just the fan blades basically.
Any gems of wisdom anyone?