Need more specifics...

Does the board have an 'on board' graphics adaptor... what cards are not recognised?

Graphics cards can be PCI (rather old), AGP (not so common nowadays) or PCI Express (not the same thing as PCI).

AGP has the complication of 2x, 4x and 8x varieties, so the board has to support that type - 8x won't work on a board that only supports 2x and 4x, for example.

PCI express has similar complications, further complicated by some cards needing two slots...

So... what board, specifically, what CPU, and what cards?

Check your power supply, too...

(going to bed now... nighty bye!)