My Dell Vostro 3450 Notebook
When I put windows 10 on it and install the video card .. from the black screen
You haven't supplied all the info needed INFORMATION REQUIRED WHEN POSTING A QUESTION but if you have the standard Vostro 3450, it does not meet Microsoft's minimum requirements for Windows 10. The Intel graphics are not supported...which ruins the switchable graphics. There is no settings or magical tricks to make the laptop usable. Reverting to the OS the laptop was designed for will give you a fully functioning computer.
Laptops with switchable AMD/Intel graphics Windows 10 support
Retrieving data ...