Screen won't display new AMD PC, has no operating system

I bought a new Gear AMD PC so It has no operating system so I want to install the disk. My dad gave me his Samsung screen.
At the store I bought a Graphic Card (GeForce GT 520) and they also installed that when i bought it and they assured it was compatible and my tech boyfriend was with me and approved.

The screen on and it displays no connection when turned on and not connected , then I conected it and it's just all black and the screen light is blinking and it does that when the pc is off. When I turn the PC on nothing happens. The light still blinks as if it were off or asleep, but I hear the pc turning on and all.
wtf? Help? I already checked like 10 times if it's correctly connected.
 
Take the computer back to the store along with the Samsung monitor, and have them check the computer
 
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