Dell OptiPlex XMT 5133 does not see PCI/ISA 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.

I am not very familiar with hardware, just what
I've seen inside the few computers I owned, but
this one is different from all others: it has two boards
inside. One seems to be the mother board, with
the processor and the RAM memory on it, and
the video card built in - on the back of the case
it has all the plugs for monitor, keyboard, mouse.
Separate and on top of the mother board there
is another little board, with only the ISA and PCI
slots on it - on the back of the case there are
separate spots for the plugs of the modem, sound
card and network card, I mean in a separate area
than the plugs for the mother board.

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.