Monitor wont pick up DVI connection/Computer wont read graphics card?

Hello, so recently my computer has been doing this thing, when I start up my pc it wont connect to DVI connection, but only VGA, but it does not pick my up proper graphics card, only an intergrated one, but when it goes back to DVI it picks up the graphics card, why is this? but for some particular reason the monitor will not pick up the DVI? my graphics card works fine, the fans are still spinning etc.
Thanks.