USB in Windows depends on system disc being master

Solution 1:

Different BIOSes work differently. It may be attributed to a Boot Order, whether configurable or not, or it might be attributed to your USB hard drive volume being marked as an Active (bootable) partition, while your primary drive is not or takes second fiddle to removable Active partitions.

If you don't intend to boot from a drive, be sure to remove the Active flag. Use DISKPART (command window) to accomplish this:

Open Start, type CMD, right-click cmd.exe or 'Command Prompt' and select 'Run as administrator'.

Follow along these commands:

  DISKPART
  LIST VOL  (aka LIST VOLUME)
  SEL VOL {number or drive letter}  (aka SELECT VOLUME)
  DET PART  (aka DETAIL PARTITION)
if it says 'Active: Yes', then type:
  INACTIVE

Repeat for other volumes that do not need to be Active bootable partitions. Check to make sure your C (boot) volume is, in fact, Active. If not, mark it so with the ACTIVE command. This is how your BIOS should scan to determine which drive to boot from, when it's in doubt.

You can always mark a partition as Active within Windows Disk Management, but DISKPART is the only practical way to undo that action and remove the Active flag.