Onboard video chipset: Nvidia GTX285 compatability

If a motherboard has an onboard video chipset, can you still install a graphics card into the PCI Express slot and use it? For example, if one were to purchase a motherboard with an ATI onboard video chipset, would it still be compatible with an Nvidia GTX 285?

I think I need a new motherboard for under $100. I built my computer over 2 years ago and the motherboard had an Nvidia nForce 780i SLI chipset, but I can't seem to find any motherboard on newegg.com(where I generally shop for computer parts) that has this chipset.

Any recommendations on a good, cheap mother board that can support 4 gig DDR2 RAM, Socket LGA 775, Intel Q9450 processor, and an Nvidia GTX 285 graphics card?
 
I think I may have fried my mother board. Its either that or the CPU. I posted a description of my problem here:

I posted a description of my problem in the Windows BSOD, Freezing, Restarting Help forum. I'd provide the link but unfortunately I can't because I am not a level 5 or higher here yet.

I'm not getting any BIOS beeps whatsoever.

So I can use a Nvidia Graphics card with an ATI board?
Is there any physical way to tell if a motherboard or CPU is destroyed? I've looked both over and they look fine to me.

My setup is old but I can't afford to upgrade. I have to cheaply make do with what I have and add whatever component is faulty.
 
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