I continue my journey with this motherboard.
The A7M266-D mobo has 3 PCI (32bit 5V) and 2 PCI 64bit (3.3V) slots.
I read somewhere that the PCI 64bit can be used for normal PCI 32bit card. The first problem was the notch.

Most of the 32bit PCI card, which are 5V capable, are notched on the far side. The 3.3V cards are the near side. ( With "far" and "near" I am referencing the steel plate of the card.)
There are some hybrid cards, which have 2 notches on the PCI slot, which I assume capable of work in both system. I have e.g a 3COM ethernet card and a intel ethernet card with 2 notches.

I trided to put these hybrid cards in the 3.3V PCI 64bit slot, but the system does not boot at all. If I remove the card, everything working fine. Note: The cards are working in the PCI 32bit slot.
There is no setup in the bios regarding the 64bit PCI.

What is going on? I was told, a 32bit card should work on the 64bit slot.