GPU is Asus GTX 780, but dxdiag, it shows only VGA card for video, even though device mgr shows a list of GPU drivers present.

I tried downloading Asus's site, but it's a zip file, & I get prompted to purchase WinZip when I try to extract it (not doing it unless I have no other choice).  What am I supposed to do to get the hardware I bought to work?

If you're running Windows, right click, extract all. It's built in.

Edit I see you've tried to extract it. DL it from Nvidia's site. It should be an executable file and the newest.

Like David said no need to buy WinZip. 7zip is free and isn't a bad program to have on your PC though. But windows should do it no problem.

Also, just want to make sure you enabled the card in the BIOS settings.

So, I once again ferreted out the solution.  Turns out that Nvidia's GPU driver installer is notorious for failing, so much so that there are Youtube channels out there on how to fix it.  The solution involves bypassing the Nvidia installer & using Device Mgr to install the driver manually.  For those who might find themselves in a similar bind, here's the fix I used:

1. Download the driver(s) off Nvidia's site.  The installer will automatically run, but then fail w/o offering a reason.
2. Open up Windows Device Manager (Start\Control Panel\Hardware & Sound\'Devices & Printers' -> select 'Device Manager').
3. Select 'Display Drivers' in the list tree & select/highlight the GPU card to be updated.
4. Click on 'Update Driver Software' icon located in the menu bar above -> opens a menu window.
5. Choose the 'Browse' option & input the path (default download path should be C:\Nvidia\Display Driver), check 'Include subfolders' option.
6. Click 'Next', to run the install.

You can check for the systems overall setup by typing 'DxDiag' in Start\Search option, & selecting 'Next Page' to run through the setup ocnfigs.  The graphics display mode should indicate the card being run (VGA will be the default if the specific Nvidia driver(s) aren't installed).