when you inserted the MMU part of the upgrade.
You might have bent one or two of the mmu pins (squashing it) I did this myself but I lost the video display completley.
Pop out the MMU adaptor
Then pop out the MMU chip (remember where the dot on the chip is pointing).
Apply a little pressure onto the pins as to squash the pins downwards so to expand the pins.
Reinsert the chip (the correct way around)
and carefully reinsert the MMU.
You might have to try a couple of time to get it to work.
This upgrade left me with out an STFM for 7 years even a computer shop could not fix it!
Once I have got a 2nd STFM I have a play and found this to be the fault.
Whilst the computer is on you could try carefully applying movement to the adaptors to see the the display changes. just be careful (electric and all that).
