I have LG flatron 915ft plus display(i got it free from my friend and it is like new) but there is problem.When i make my 3d models or other stuff my display goes suddenly black.
it feels like i falling in to black hole-quite nasty feeling.I dont use any sreensavers or etc.
Or is it my graphcard(gf6200) or motherboard(Asrock).Or it is some other failure?
And that blackness is very short time 1-2 seconds(and all cables etc are connected tight)

It sounds like driver issue, or something with openGL, D3D, or directX
Update your drivers for the gfx card and monitor from the manufacturers website.
Get the latest dirextX

Also check that you are doing your 3d editing at the same resolution as the windows desktop, sometime changing resolution will make your screen go balsk for a while