T5500 not booting / diagnostic advice please

Just got a new to me T5500 workstation, has been working fine until I decided to add a PCI card. I went inside and added the card, but also pulled the DIMM to chack what was installed as I was planning to add additional memory,

Symptoms are DELL slash screen appears, progress bar move to complete, then black screen and system is hung. Revered all the changes and no different. I can hit f2 and some text says starting bois config but the black screen and hung, F12 I get to the one time boot menu I can select up and down the list, but if I hit enter hangs.

No beeps, diagnostic lights flash during POST, and when it hangs its steady 123 light and solid green power button light.

Tried:

Password / CMOS reset  - after DELL splash screen RAID config utility prompt no appears

Back up battery out  - additional on screen message as disk bios finds disks

F8/F11 - do nothing

Disconnected all sata disks 

Removed memory and tried single sticks in DIMM0, with no memory I get 1-1-3 beeps

Wont boot from internal DVD, usb, usb floppy or SATA 0 & 1 swapped.

checked seating of cables cards, etc.

Other than the differences clearing the CMOS made nothing has got me close to getting it to boot again.

Kind of resigned to the fact I have killed the mother board. But hoping maybe its corrupt bios and the is some little know way to reflash it. But given I can't boot from any media seem like a slim chance.

Anyway before I go hunting a replacement mother board thought I try a post here just in case. Any ideas appreciated.

Cheers

Adrian