Solved! Alienware 15 R4: "No bootable devices found." & "Boot failure on device"

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Jan 7, 2019
So I won this Alienware 15 R4 and it arrived without a hard drive. No biggie, that's in my ballpark, I go and buy a normal 500GB Toshiba hard drive and install it in the laptop. After I turn it on, though, it shows the Alienware loading screen as normal and then shows a black screen with text in the top left saying "<Checking media presence...>". After about 30 seconds, it then enters into SupportAssist and runs a hardware scan. It usually takes about a minute or 2 and always comes back with 1 of 2 different results. It'll either have a red cross next to some text that says "Boot failure on device." or it will complete the scan and say "No bootable devices were found!" I'm really useless beyond the point of installing the hard drive. Any help would be appreciated.
Here are the specs if that helps with anything:
Alienware 15 R4
Intel i7 8750H @ 2.2GHz
Nvidia Geforce GTX 1060 6GB
Toshiba HDWK105 500GB
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