My primary objective is to make a pc boot from usb flash drive and launch the standard debian installer.
Check & make sure your BIOS is set to "Boot from USB" (sometimes also known as "Boot from Removable Device").
Get boot.img.gz (stable linked below):
unzip & place raw content inside the UNMOUNTED flash drive:
zcat boot.img.gz > /dev/sdc (assuming sdc is yours).
Above comment unzips and appends boot.img to your Usb Key.
Get current netinst iso image:
Above command wgets etch-netinst.
Now copy-paste the ISO file image to the flash drive (as is).
All good - you may now disconnect your new Debian Installer USB Key and spread the Debian word everywhere!
If it works, it will boot a kernel and find automatically the iso image then proceed with the install process as usual.
During partitioning, your flash drive might be listed before your HDD(s). In other words, your USB Key might take precedence and be reported as /sda (while your other internal HDDs might show-up as /sdb,/sdc, etc.).
To mitigate the above issue, goto your BIOS then Set "Boot Removable Devices First" to "Disabled".