In order to boot from my bootable USB drive to install Windows 7 Ultimate 64-bit, I disabled the HDD in the boot order so it only loads the USB. However, after I changed some settings as well (this computer had windows 8 preloaded but it would go really slow) and then I can't access my BIOS anymore. Without the HDD enabled in the boot order, my computer does a reboot into the installation, when the USB is connected. When no USB is connected, it just goes into a boot loop where it shows the first loading screen, turns off, turns on, and continuing.
My computer is a Samsung Laptop and I've tried pressing every button on my keyboard but nothing seems to work...
Not sure why you had to disable HDD rather than just move USB drive to first boot priority but from what I understand now you have a USB (external) HDD set as primary boot device and cannot access the BIOS to change the boot order so the Win7 HDD is primary, correct?
Are you able to access the BIOS with the USB drive connected?
Might just have to try different combinations and make sure you're hitting the right key (should be F2 or delete) during start-up to get into BIOS.