To understand your question.... you say after installing a new AMD gfx card your Standard VGA Adapter is missing from Device Manager ?
That is expected.
"Standard VGA Adapter" is a windows generic driver to get basic functionality on the device and to allow you to at least boot up and log into windows.
You dont mention if you had an old card in, or anything, it is hard to tell what you mean by Standard VGA Adapter is missing....was it allways like that ?
Or did you install the drivers for the first time, and windows replaced the standard driver with the proper manufacturer driver?
What device is listed under Display Adapters?