Dell OptiPlex XMT 5133 - issue with ISA/PCI slots

Hi there,

I have an old Dell OptiPlex XMT 5133 computer,
and recently I had to reinstall the operating system -
Windows NT 4.0, service pack 6.

This computer is peculiar: it has two boards inside.
One seems to be the mother board, with the processor
and the RAM memory on it. Separate there is another
little board, with only the ISA and PCI slots on it.

This is all good and nice, the problem is that after
re-installing the operating system, the cards that are
plugged in the ISA or PCI slots are not visible to
the computer anymore - like there is no link now
between the little board and the mother board.

I don't remember unplugging anything, if that is the
case I will try and see if there are any loose ends,
but I think it is not a hardware problem, because in
a way the computer sees new hardware but it is not
able to do anything about it.

What I did is I bought another network card, the old
one was a ISA one, the new one is a PCI one - after
I switched them, at boot time, I get a:
"Plug and Play error,
Press F1 to continue, F2 to go to settings ...".

If I press F1 it continues booting and, when it's up, it
still doesn't see the network card, and if I press F2 we
go to BIOS settings, where I'm lost, because everything
seems normal to me, I've read all the entries but none
seemed to have anything to do with ISA or PCI.

If anybody has any ideas please help!

Thank you,
Gerula.