I only have one on board video adapter. can I buy a video card to try in the slot on the mother board?

I have tried with my other desktop video card, it doesn't fit in any slot, so what kind of video card I should buy?|||you need a PCI-E slot for a video card. If you haven't got a manual, you can download one from the manufactuer's website, if you know the make and model of motherboard. If the board hasn't got one then you need a new motherboard. Remember the word "compatibility"|||Depending on the motherboard it can be either AGP (older) or PCI-E. If what you have is AGP then you need PCI-E