Issues with my new PC build

Picked up a PC from Best Buy, it arrived yesterday and turned on fine. Today I plugged everything in—keyboard, mouse, controller, monitor via HDMI—and it boots up just long enough to shut itself off immediately.
Now it does this constantly, even when nothing is plugged in but the power cord.



Could this be a GPU issue? I was reading online about some older GTX 960 cards having trouble with HDMI connections.
I already tested all my cables and the monitor on an older PC, and they work perfectly.

Have you tried hooking up the monitor using a DVI or VGA connection instead? If the drivers haven't been properly installed yet, I have a feeling the HDMI port isn't going to cooperate at all.

I tried that too. Turns out the issue was just the frame; I popped it out and reseated it, and now everything works perfectly.