The expansion connector could have contacts with a light covering of corrosion. It might help to insert, remove and re-insert the card and make sure it is parallel and fitting snug.
I cut my shielding back when I had a Blizzard 1230-IV but in reality the shield is nowhere near the Blizzard. The connector is surrounded by a black plastic block.
If you have a hard disk on the internal interface then try removing this and testing (my 1230-IV hated an old Quantum Daytona Go-Drive 2.5").
Try also, removing and refitting the SIMM and taking away all things that could drain power from the motherboard (flicker-fixers, joysticks, PCMCIA cards etc.)
