New CPU not recognizing custom OS boot disk

Mar 18, 2018
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Hey all,

I built a new CPU from scratch using a build my friend has. I am new to this but successfully got everything set up - all the hardware is put together and the system is turning on to the "insert boot drive media" black screen.

One problem: It is not recognizing any custom boot disk I put in. I have made several through various methods and used them all on different computers, and they do work, but not on this CPU.

The OS is set to Windows 8.1 pro. I bought it from an online shop not knowing that I would not get a physical copy, so I am either stuck figuring out how to acquire a boot disk (can you just get an official disk somewhere in stores?) or trying to get my money back and just ordering a physical official Windows disk.

I have switched the default boot device (the computer DOES recognize the disk drive), unhooked the hard drive completely at one point, and looked everywhere and cannot figure out a specific answer, so I appreciate all the help I can get!

Intel Core i5
Motherboard - ASRock B250 M Pro4