BIOS can’t see flash drive and SSD simultaneously

I needed to switch out the motherboard, with CPU, RAM and a 1TB M.2 drive in my PC. Before pulling the motherboard, I burned a system image onto a 512 GB flash drive.

I installed my previous motherboard and SATA hard drives, but I didn’t want to risk losing any data by putting the system image ISO onto either one of them.

So, I purchased a 1 TB SSD. I connected that, and also inserted the flash drive with the system image ISO. Apparently, the BIOS was not able to see the flash drive and SSD at the same time — only the SSD.

I powered down, removed the SSD, and restarted … the flash drive was immediately recognized.

I don’t know why the flash drive and SSD cannot be seen together. The SSD is on a SATA channel, while the flash drive is USB.

I’m assuming I cannot hot-plug the SSD after the system is running. How can I get the system to recognize both drives simultaneously, so I can transfer the system image ISO?

Thanks in advance,
- David G.

Gigabyte FX AM3+ mobo
AMD 6-core 3.8 GHz CPU
16 GB DDR4 RAM
Windows 10

Just added:
PNY USB 3.2.2 512GB flash drive
SanDisk 1 TB SSD

With the SSD connected, I cannot see the flash drive in BIOS. I can get the flash drive to show on the boot menu, but ONLY with the SSD disconnected.

Yes, I realize AM3 is a socket type, I was just explaining what type of processor I had.

“Ponto” was a typo. It was supposed to simply say, “I burned a system image onto a 512 GB flash drive.” I used AOMEI to burn the system image.