I encountered a similar problem with my Intel Desktop. Whereas my other PCs only require me to use the F12 key to choose a USB flash card as the boot device, or to place it first in the boot configuration, the Intel PC chooses to consider flash devices greater than 4GB (or maybe it's 2GB?) as drives. In order to have such devices appear in the boot configuration lineup, you have to rearrange them first in the drive lineup (because only so many places are available, IIRC). This is all a bit fuzzy because it's been a few months since I last dealt with this problem.